JPH0450074B2 - - 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 coagulating and separating and removing these substances. (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 about 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 shortcomings of the conventional technology and meet the above-mentioned demands, the present inventor has conducted extensive research on biological treatment methods for wastewater, and has found that during anaerobic agitation and denitrification treatment while wastewater is flowing into the aeration tank. By simply adjusting the redox potential of the mixed liquid during anaerobic agitation to a predetermined value, the conventional batch-type wastewater biological treatment equipment can be used as is, achieving high efficiency that could not be achieved with conventional methods. The present invention was completed based on the finding that nitrogen and phosphorus in wastewater can be treated and removed at the same time easily and at low cost. (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 mixture of wastewater and activated sludge in the aeration tank is subjected to anaerobic agitation by adjusting the redox potential of the mixture to -250 mV or less, and the anaerobic agitation during denitrification treatment performed after aeration treatment is carried out in the aeration tank. This biological treatment method for wastewater is characterized by adjusting the redox potential of the mixed liquid in the range of -150 mV to -250 mV. 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 mixture of wastewater and activated sludge in the aeration tank is subjected to anaerobic stirring by adjusting the oxidation-reduction potential of the mixture to -250 mV or less. The feature of anaerobic stirring during denitrification treatment after aeration treatment is to adjust the redox potential of the mixed liquid in the aeration tank to a range of -150mV to -250mV. According to
The objectives of the present invention have largely been achieved. That is, according to detailed research by the present inventor, raw wastewater to be treated flows into an aeration tank, and a mixed liquid of the raw wastewater and activated sludge that flows into the aeration tank is heated at a temperature below the predetermined redox potential. By performing anaerobic stirring, the hydrolysis of ATP in the mixture proceeds quickly and phosphorus is released. Under aerobic conditions that are followed by aeration, ATP is efficiently produced and microorganisms release phosphorus in excess. On the other hand, by performing the subsequent denitrification treatment with the redox potential of the mixture in the aeration tank within the specified range, under the anaerobic conditions of this denitrification process, nitrogen in the form of nitrite or nitrate is removed. Due to the presence of
Therefore, it has been found that the phosphorus content of sludge is maintained at a high concentration through a series of biological treatment steps, and as a result, the phosphorus removal effect is maintained at a significantly high level. In the present invention, in order to keep the oxidation-reduction potential of the mixed liquid in the aeration tank below a certain value, that is, -250 mV or less, the mixed liquid in the aeration tank is anaerobically stirred during the inflow of wastewater, and as time passes. Since the oxidation-reduction potential decreases, if the inflow time of the wastewater is increased or if the wastewater is allowed to flow in for a short period of time,
By continuing anaerobic stirring until the redox potential of the mixed liquid drops to a predetermined value, the redox potential of the mixed liquid can be reduced to −250 mV or less.
Generally, by maintaining such an anaerobic state for about 1 hour or more, the oxidation-reduction potential of the mixed solution can be reduced to -250 mV or less. In addition, the redox potential of the mixed solution in the denitrification process can be adjusted in the same way as above, by adjusting the anaerobic stirring time during the denitrification process, by adding a hydrogen donor during the stirring, or by a combination of both. While monitoring the redox potential of the mixed solution,
The redox potential can be controlled within the range of -150mV to -250mV. The oxidation-reduction potential of such a liquid mixture can be easily measured using an ordinary oxidation-reduction 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 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 to a storage tank 2, where it is temporarily stored. 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 oxidation-reduction potential of the mixed liquid is adjusted to the above-mentioned value or less. The method is to perform stirring and mixing as is, that is, anaerobic stirring, and the raw wastewater and activated sludge are thoroughly mixed by this anaerobic 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, and after confirming that the oxidation-reduction potential of the mixed liquid is below a predetermined value, aeration is started 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. 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. 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 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 the 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, 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 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. 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, By controlling the redox potential of the mixed solution of wastewater and activated sludge to below -150 mV and performing anaerobic stirring, phosphorus is effectively released by hydrolysis of ATP, and then in an aerobic state by aeration.
ATP is produced and the sludge is kept in an efficient state of phosphorous overload. In addition, the anaerobic state in the denitrification process is controlled to a redox potential within a certain range, so nitrite or nitrate nitrogen is present, so microorganisms that have ingested an excessive amount of phosphorus will not be able to 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 changes the oxidation-reduction potential of the mixture of wastewater and activated sludge in the wastewater inflow process and the mixed liquid in the denitrification process to an anaerobic state under the conditions described above. Even if it is retained, it will not have any 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. Glucose 360mg/, starch 200mg/
, peptone 160mg/, potassium dihydrogen phosphate 30
mg/, urea 58 mg/, BOD 500 mg/, total nitrogen
The anaerobic conditions for phosphorus release and denitrification reactions were investigated using synthetic wastewater containing 40 mg of total phosphorus and 12.5 mg 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 decreased to -100 mV in about 2 hours after starting anaerobic stirring, and -150 mV in 5 hours, resulting in a decrease in the redox potential and a denitrification reaction. The reaction time was slow, and 4 mg of nitrate nitrogen remained after 5 hours, 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 decrease in redox potential, denitrification rate, and phosphorus release rate depending on the type of hydrogen donor; The results showed that the release of phosphorus from activated sludge proceeded under anaerobic conditions with a redox potential of -250 mV or less. When performing biological denitrification and dephosphorization by combining the anaerobic and aerobic processes, there is a large difference in the optimal anaerobic degree between the denitrifying bacteria and the dephosphorizing bacteria in the anaerobic process. In order to perform denitrification and dephosphorization stably, it is necessary to maintain the optimum anaerobic level for denitrifying bacteria and dephosphorizing bacteria during the nitrification process.
Therefore, in the present invention, by controlling the redox potential to -250 mV or less in the anaerobic process when raw water is injected, the optimum anaerobic degree for the dephosphorizing bacteria is created, and in the anaerobic process when hydrogen donors are added. By controlling the redox potential to between -150mV and -250mV, the denitrifying bacteria can reach optimal anaerobic conditions, making it possible to maintain high activity levels of the denitrifying bacteria and dephosphorizing bacteria, resulting in stable nitrogen production. , phosphorus simultaneous treatment 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 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 nitrogen and phosphorus composition of the wastewater, and since nitrogen and phosphorus were excessive (BOD: nitrogen: phosphorus = 100:10.5:2.0), treatment using the normal activated sludge method The composition of the wastewater is such that nitrogen and phosphorus remain in the wastewater.

【table】

[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.
That is, first, wastewater is allowed to flow from the storage tank into the aeration tank within 2 hours, and during the inflow time, the redox potential is controlled to -250 mV or less by anaerobic stirring to release excess phosphorus into the 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, add isopropyl alcohol as a hydrogen donor.
was added for 0.25 hours, and then the redox potential was controlled at -150 mV to -250 mV by anaerobic stirring for 6 hours.
Allow denitrification reaction to proceed. Then, reaeration for 1 hour,
Sedimentation takes 2 hours, treated water discharges for 1 hour, and sludge is pulled out for 0.5 hours, completing one treatment in 24 hours a day. The continuous water flow experiment was carried out for about one month, and the oxidation-reduction potential and nitrogen and phosphorus concentrations were
An example of changes over time in days is shown in Fig. 3. In Figure 3, in the anaerobic process when raw water flows in, the redox potential of the aeration tank mixture is controlled to -250 mV or less, and phosphorus is released from the activated sludge, and in the next aerobic process by aeration, phosphorus is released. Ingestion and nitrification reactions proceed rapidly, and even in the anaerobic process due to hydrogen donor addition, the redox potential of the mixed liquid is controlled to the set value of -150mV to -250mV.
It has been shown that although the denitrification reaction is proceeding rapidly, phosphorus release from the activated sludge is not occurring. Fig. 4 shows the changes over time in the treatment test results under such treatment conditions. The treatment results during this implementation 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/. The removal rate of nitrogen components was also 95-98%, and the TN concentration in the treated water was always below 10 mg/. Furthermore, the removal rate of phosphorus components was 94 to 98%, and the phosphorus concentration in the treated water was always below 1 mg/. 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 the drawing]

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 mixture of wastewater and activated sludge in the aeration tank is subjected to anaerobic stirring by adjusting the oxidation-reduction potential of the mixed liquid to -250 mV or less, and the desorption performed after the aeration treatment. Anaerobic stirring during nitrogen treatment lowers the oxidation ring potential of the mixed liquid in the aeration tank from −150 mV to −
A biological treatment method for wastewater, characterized by adjusting the voltage to a range of 250mV. 2. The biological treatment method for wastewater according to claim 1, wherein the redox potential is controlled by adjusting the time of anaerobic stirring in the aeration tank or by adding a hydrogen donor.