JPH0450075B2 - - 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, a method for biologically treating nitrogen and phosphorus in wastewater at the same time. 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 nitrogen from wastewater. It consists of two steps: the process of oxidizing various nitrogen compounds to nitrite or nitric acid, and the denitrification process of reducing the nitric acid or nitrous acid produced in the nitrification process 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 needs, the present inventor has conducted extensive research on biological treatment methods for wastewater, and has found that during anaerobic agitation while wastewater is flowing into the aeration tank, and during denitrification. This could not be achieved with conventional methods by simply controlling the total concentration of nitrite and nitric acid in the mixed solution during anaerobic agitation during treatment to a predetermined value, and by using conventional batch-type wastewater biological treatment equipment as is. The present invention was completed based on the discovery that nitrogen and phosphorus in wastewater can be treated and removed at the same time easily and at low cost with unprecedented efficiency. (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, during which the wastewater flows into an aeration tank.
The mixed liquid of wastewater and activated sludge in the aeration tank is subjected to anaerobic stirring by controlling the total concentration of nitrite and nitric acid in the mixed liquid to 0.2 mg/l or less, and the denitrification process is completed after the aeration process. The total concentration of nitrite and nitric acid in the mixed solution in the aeration tank during the anaerobic process is 0.2 mg/l to 1.0.
This is a biological treatment method for wastewater, which is characterized by controlling the amount within a range of mg/l. 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,
While the wastewater is flowing into the aeration tank, the mixed liquid of wastewater and activated sludge in the aeration tank is anaerobically stirred by controlling the total concentration of nitrite and nitric acid in the mixed liquid to 0.2 mg/l or less. The second feature is that
Calculate the total concentration of nitrite and nitric acid in the mixed solution in the aeration tank during the anaerobic process at the end of denitrification treatment performed after aeration treatment.
The objective of the present invention is mainly achieved by controlling the content within the range of 0.2 mg/l to 1.0 mg/l. That is, according to detailed research by the present inventor, raw wastewater to be treated flows into an aeration tank, and the total concentration of nitrite and nitric acid in the mixed solution of raw wastewater and activated sludge that flows into the tank is 0.2mg/ By performing anaerobic stirring in the aeration tank with the temperature controlled to below 100 liters, the hydrolysis of ATP in the mixture proceeds quickly and phosphorus is released, and under aerobic conditions due to the subsequent aeration, ATP is efficiently microorganisms can take up too much phosphorus;
By controlling the subsequent denitrification treatment so that the total concentration of nitrite and nitric acid in the mixed solution in the aeration tank is within the specified range at the end of the denitrification process, the anaerobic conditions for this denitrification process can be improved. Due to the presence of favorable concentrations of nitrogen in the nitrite or nitrate form,
Polyphosphate-accumulating microorganisms are able to maintain normal respiratory metabolism and the ingested phosphorus is not released, thus maintaining the phosphorus content of the sludge at a high concentration through a series of biological treatment steps, resulting in the reduction of phosphorus. It was discovered that the removal effect was maintained at a significantly high level. In the present invention, the total concentration of nitrite and nitric acid in the mixed liquid in the aeration tank is kept below a certain value, that is, 0.2
mg/l or less, by anaerobically stirring the mixed solution in the aeration tank while the wastewater is flowing in, the total concentration of nitrite and nitric acid decreases over time, so the time required for the wastewater to flow in is lengthened. Alternatively, if wastewater is introduced in a short period of time, anaerobic stirring can be continued until the total concentration of nitrite and nitric acid in the mixture drops to a predetermined value. The total concentration can be 0.2 mg/l or less. Generally, by maintaining such an anaerobic state for about 1 hour or more, the total concentration of nitrite and nitric acid in the mixed solution can be reduced to 0.2 mg/l or less. In addition, the total concentration of nitrous acid and nitric acid in the mixed solution at the end of the denitrification process can be controlled in the same way as above, by controlling the anaerobic stirring time during the denitrification process or by adding a hydrogen donor during the stirring. While monitoring the total concentration of nitrite and nitric acid in the mixed solution, the total concentration of nitrite and nitric acid is controlled within the range of 0.2 mg/l to 1.0 mg/l by a method or a method of combining both. be able to. The total concentration of nitrous acid and nitric acid in such a mixed solution can be easily measured using an ordinary nitrate concentration meter or nitrite concentration meter. 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 containing excessive amounts of elemental elements and phosphorus. If so, any wastewater can be treated. Especially when the BOD concentration is 100mg/l or more and 5000mg/l or less,
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-mentioned 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 is led to the storage tank 2,
It is temporarily stored here. The raw wastewater in this storage tank is preferably agitated and mixed by aeration, mechanical stirring, a stirring pump, etc. for the purpose of homogenization. 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 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 the total concentration of nitrite and nitric acid in the mixed liquid is kept at the above-mentioned value. This is to perform stirring and mixing, that is, anaerobic stirring, while controlling as follows. The control method is to always control the nitrite and nitric acid concentrations of the mixed solution to 0.2 mg/l or less by adjusting the anaerobic stirring time in the aeration tank based on the measured values of the nitrite and nitric acid concentrations. The anaerobic stirring time may be adjusted by adjusting the time of the wastewater inflow process by reducing the amount of wastewater flowing in, but it is also possible to simply perform anaerobic stirring without starting aeration after the inflow is complete. Either method is fine. This anaerobic stirring thoroughly mixes the raw wastewater and activated sludge. 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, and after confirming that the total concentration of nitrite and nitric acid in the mixed liquid is below a predetermined value, aeration is started in the aeration tank. Aeration may be performed using any conventionally known method, for example, using a blower 7.
This can be done by means of air sent through the pipe 8. 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. Normally, the pH of the aeration liquid at the end of the treatment should be maintained at 6.5 to 9.5. After the nitrification reaction is completed and the aeration process is completed,
Anaerobic stirring is carried out in accordance with the features of the invention described above. In this anaerobic stirring, a hydrogen donor is added into the aeration tank from the chemical injection path 10 as needed, and the stirring pump 6 in the aeration tank performs anaerobic stirring without aeration to advance the denitrification reaction. , to separate nitrogen as nitrogen gas. During the denitrification process, the nitrite and nitric acid concentrations in the mixed solution are measured using a nitrite meter or nitrate meter in the aeration tank, and at the end of the denitrification process, the concentration is always in the range of 0.2 mg/l or more and 1.0 mg/l or less. The anaerobic stirring process is controlled as follows. The control method is to keep the nitrite and nitric acid concentrations in the mixed solution at the end of the denitrification process at 0.2 mg/l or higher at all times by adjusting the amount of hydrogen donor added based on the measured value of the nitrite meter or nitrate meter. It may be controlled within a range of 1.0 mg/l or less, or it may be controlled by adjusting the anaerobic stirring time in the denitrification step after addition of a predetermined amount of hydrogen donor. As the hydrogen donor used in this anaerobic step, industrial chemicals such as methanol, ethanol, acetic acid, and isopropyl alcohol, or waste liquids similar to the composition of inflow wastewater but not containing excessive amounts of nitrogen and phosphorus can be used. The amount of hydrogen donor added in this anaerobic stirring step is such that nitrite and nitrate nitrogen produced by the nitrification reaction are removed from the system as nitrogen gas by the denitrification reaction.
The amount to achieve the above-mentioned predetermined concentration is sufficient. The anaerobic stirring time is also set to be the time necessary for the total concentration of nitric acid and nitrous acid to reach the predetermined concentration. 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, and the reaeration process is completed. After that, the stirring is stopped and 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 or before or after discharging the treated water from the aeration tank 5, a predetermined amount of sludge is drained from the sludge pipe 12 into the sludge storage tank 13, and the pipe 14 is subjected to treatment such as dewatering or carried out as is. dispose. 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, and during the treatment of wastewater, while the raw wastewater is flowing into the aeration tank, the raw wastewater is By controlling the total concentration of nitrite and nitric acid in the mixed solution of nitrite and activated sludge to 0.2 mg/l or less and performing anaerobic stirring, phosphorus is effectively released by hydrolysis of ATP, and then ATP is produced under aerobic conditions through aeration, and the sludge is maintained in a state where it can efficiently uptake excess phosphorus. In addition, the anaerobic conditions in the denitrification process are controlled to a total concentration of nitrite and nitric acid within a certain range, so microorganisms that have ingested an excessive amount of phosphorus can carry out normal respiratory metabolism. No phosphorus is released even under the conditions. Therefore, in the present invention, compared to conventional methods, the phosphorus content of sludge can be maintained at a high level until the end, so that phosphorus can be removed stably and to a high degree simply by disposing of the excess sludge at the end. In addition, in the method of the present invention, in addition to the above-mentioned removal of phosphorus, the total concentration of nitrite and nitric acid in the mixed solution of wastewater and activated sludge in the wastewater inflow process and the mixed solution in the denitrification process is Even if the conditions are maintained, there is no adverse effect on biological nitrogen nitrification and denitrification reactions. 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. The excellent effects described above were proven by the following experiment. Glucol 360mg/l, starch 200mg/l using bench scale experimental equipment with an aeration tank capacity of 20l.
l, peptone 160mg/l, potassium dihydrogen phosphate 30
mg/l, urea 58mg/l, BOD500mg/l, total nitrogen
Anaerobic conditions for phosphorus release and denitrification reactions were investigated using synthetic wastewater containing 40mg/l and 12.5mg/l of total phosphorus. In the experiment, the nitrification reaction due to aeration has been completed, and the activated sludge has taken up an excessive amount of phosphorus, and the aeration tank mixture is anaerobic by adding inflow raw water and isopropyl alcohol as hydrogen donors for the purpose of the denitrification reaction. The conditions were changed and changes over time in the redox potential and the nitrate nitrogen and orthophosphoric acid concentrations during anaerobic stirring were measured. The results are shown in FIG. Here, when the hydrogen donor was added, the amount added was twice the theoretical equivalent required for the denitrification reaction of nitrate nitrogen in the waste water. As a result, when anaerobic stirring was performed without adding a hydrogen donor, the redox potential was -100 mV approximately 2 hours after the start of anaerobic stirring, and the nitric acid concentration was 9 mg/l.
-150mV in 5 hours, nitric acid concentration 4.0
mg/l, the reduction in redox potential and denitrification reaction were slow, and even after 5 hours, 4 mg/l of nitrate nitrogen remained, and no release of phosphorus from the activated sludge was observed. On the other hand, when a hydrogen donor is added, there are differences in the reduction in redox potential, denitrification rate, and phosphorus release rate depending on the type of hydrogen donor, but at the end of the denitrification reaction, the redox potential is −150 mV. ～−
250mV, that is, the nitric acid concentration is 1 mg/l or less and
No phosphorus release occurs under anaerobic conditions of 0.2 mg/l or more;
The release of phosphorus from activated sludge occurs when the redox potential is -
The results showed that the process progressed in an anaerobic state with a nitric acid concentration of 250 mV or less, that is, a nitric acid concentration of 0.2 mg/l or less. In this way, when performing biological denitrification and dephosphorization by combining anaerobic and aerobic processes, there is a large difference in the optimal anaerobic degree between denitrifying bacteria and dephosphorizing bacteria in the anaerobic process. , stable denitrification,
In order to perform dephosphorization, it is necessary to maintain optimal anaerobic conditions for denitrifying bacteria and dephosphorizing bacteria during the nitrification process. Therefore, in the present invention, in the anaerobic process when raw water flows in, the total concentration of nitrite and nitric acid is
By controlling it to 0.2 mg/l or less, the optimum anaerobic degree for dephosphorizing bacteria is created, and in the anaerobic process when hydrogen donor is added, the total concentration of nitrite and nitric acid is 0.2 mg/l at the end of the denitrification process. By controlling the anaerobic level to between 1 and 1.0 mg/l, the optimum anaerobic degree for denitrifying bacteria can be maintained, and the activity of denitrifying bacteria and phosphorizing bacteria can be maintained at a high level, resulting in stable nitrogen and phosphorus simultaneous production. The processing effect can be achieved. Next, the present invention will be explained in more detail with reference to Examples. Example 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 ² /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 wastewater composition of elements and phosphorus.
In addition, since nitrogen and phosphorus are excessive (BOD: nitrogen: phosphorus = 100:10.5:2.0), in treatment using the normal activated sludge method, the wastewater composition is such that nitrogen and phosphorus remain in the treated water.

[Table] Isopropyl alcohol was used as the hydrogen donor in the denitrification process, and the amount of injection was the theoretical equivalent required for denitrification. The processing time schedule is as follows.
In other words, first, wastewater is flowed into the aeration tank from the storage tank within two hours, and the total amount of nitrite and nitrite is controlled using a nitric acid and nitrite measuring meter that can continuously measure the water. Concentration 0.2
mg/l or less to release excess phosphorus into activated sludge. During the subsequent 12-hour aeration process, activated sludge ingests excessive amounts of phosphorus in the wastewater, and oxidizes and decomposes nitrogen components in the wastewater into nitrite or nitric acid. Next, isopropyl alcohol is added as a hydrogen donor, and then the denitrification reaction is allowed to proceed by anaerobic stirring for 6 hours, and the total concentration of nitrite and nitric acid is reduced.
The denitrification reaction is controlled to 0.2 mg/l to 1.0 mg/l to complete the denitrification reaction. After that, 1 hour of reaeration, 2 hours of sedimentation, 1 hour of discharge of treated water, and 0.5 hour of sludge extraction are carried out, completing one treatment in 24 hours a day. The continuous water flow experiment was carried out for about one month, and an example of the daily changes in the total concentration of nitrous acid and nitric acid, as well as the nitrogen and phosphorus concentrations during the treatment period is shown in Fig. 3. In Figure 3, in the anaerobic process when raw water flows in, the total concentration of nitrite and nitric acid in the aeration tank mixture was controlled to 0.2 mg/l or less, and phosphorus was released from the activated sludge, and the following In the aerobic process by aeration, phosphorus uptake and nitrification reaction proceed rapidly.
Even in the anaerobic process by adding a hydrogen donor, the total concentration of nitrite and nitric acid in the mixed solution at the end of the denitrification process is controlled to a set value of 0.2 mg/l to 1.0 mg/l, and the denitrification reaction It has been shown that phosphorus release from activated sludge is not occurring, although the process is proceeding rapidly. Fig. 4 shows the changes over time in the treatment test results under such treatment conditions. The treatment results during this experiment period showed that the removal rate of BOD components was 98 to 99%, and the BOD concentration of the treated water was always below 20 mg/l. It also shows a removal rate of 95-98% for nitrogen components,
The TN concentration in the treated water was always below 10 mg/l. Furthermore, the removal rate of phosphorus components was 94 to 98%, and the phosphorus concentration in the treated water was always below 1 mg/l. From the above results, it is clear that the method of simultaneously treating nitrogen and phosphorus by biological treatment according to the present invention exhibits an extremely stable treatment effect.

[Brief explanation of drawings]

FIG. 1 schematically shows the treatment process of the present invention, and FIG. 2 shows the changes over time in the redox potential and the concentrations of nitrate nitrogen and orthophosphoric acid during anaerobic stirring in an example of the present invention. FIG. 3 shows the changes in redox potential and nitrogen and phosphorus concentrations over the course of one day in the examples, and FIG. 4 shows the changes in the treatment tests in the examples over time. 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. 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, the mixed liquid of wastewater and activated sludge in the aeration tank is anaerobically stirred while controlling the total concentration of nitrite and nitric acid in the mixed liquid to 0.2 mg/l or less. , and is characterized in that the total concentration of nitrite and nitric acid in the mixed solution in the aeration tank of the anaerobic process at the end of the denitrification treatment performed after the aeration treatment is controlled within the range of 0.2 mg/l to 1.0 mg/l. Biological treatment method for wastewater. 2. Biological treatment of wastewater according to claim 1, in which the total concentration of nitrous acid and nitric acid is controlled by controlling the time of anaerobic stirring in the aeration tank or by controlling the amount of hydrogen donor added. Method.