JPH037436B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Fields This invention focuses on pollutants (hereinafter abbreviated as BOD) indicated by biochemical oxygen demand from wastewater, ammonia compounds, nitrogen compounds, phosphorus compounds, etc. that cause eutrophication of sea areas, rivers, and lakes. This invention relates to a method for removing contaminated substances using a batch activated sludge treatment method. The present invention also relates to a method for acclimatizing activated sludge from continuous activated sludge treatment using redox potential (ORP) management control so that the aforementioned eutrophic substances can be removed by a batch activated sludge process. The present invention can be applied to wastewater containing large amounts of eutrophic substances, such as urban sewage, underground water, and wastewater from processing industries such as livestock, fishing, and agriculture. BACKGROUND ART Conventionally, many methods have been proposed for removing the above-mentioned eutrophic substances by batch or continuous activated sludge treatment. For example, BOD from industrial wastewater, urban sewage, etc. can be efficiently removed by controlling the amount of aeration using the ORP of the aeration tank as an index.
64896 and JP-A-54-22955, Water Treatment Technology vol23,
No. 7, P55 (1982), etc. In addition, the method for biochemically removing ammonia compounds from wastewater is to first nitrify the ammonia compounds to nitrate and nitrite compounds using an aerobic biochemical method, and then convert these nitrogen oxides to anaerobic biochemical methods. The most common method is to add a hydrogen donor such as methanol to reduce the nitrogen gas to nitrogen gas. The involvement of ORP in removing ammonia compounds by biochemical methods is shown below. In other words, in the process of oxidizing ammonia compounds to nitrogen oxides, ORP is involved. It has been clarified in Japanese Patent Publication No. 52-22916 that it is appropriate to manage these substances. The principle of removing phosphorus compounds from wastewater has not been fully elucidated, but the following is generally accepted. In other words, when activated sludge is placed in an aerobic environment and an anaerobic environment alternately, stress occurs in the activated sludge, and in the aerobic environment, excessive phosphoric acid from wastewater is taken into cells and stored in the form of polyphosphoric acid. do. The activated sludge, placed in an anaerobic environment, then releases the polyphosphoric acid stored within the cells. When such conditions are repeated, activated sludge takes up phosphorus into cells in an aerobic environment, resulting in a decrease in the concentration of phosphorus discharged in the biochemical reactor. These properties of activated sludge are used to remove phosphorus compounds from wastewater. As mentioned above, the method of removing eutrophic substances such as BOD, ammonia compounds, nitrogen oxides, and phosphorus compounds from wastewater using biochemical methods is almost an established technology. However, with the batch activated sludge method, BOD, ammonia compounds,
It is difficult to remove all eutrophic substances such as nitrogen oxides and phosphorus compounds using only the combination of the known methods described above. That is, in the batch activated sludge method, it is difficult to remove the above-mentioned eutrophic substances at once, and a combination of processes must be used to sequentially remove each eutrophic substance. Therefore, the treatment conditions of each step (e.g. ORP, PH, dissolved oxygen concentration, treatment time, etc.) and the residual amount of eutrophic substances from the previous step have an influence on the removability of eutrophic substances in the next step. Need to be clear. In particular, removal conditions for phosphorus compounds are not clearly presented. In other words, it is said to be an aerobic environment or an anaerobic environment, but no specific conditions are specified.
Therefore, it is clear that all eutrophic substances in wastewater cannot be removed by a simple combination of known techniques, and it can be said that a technique for removing eutrophic substances by the batch activated sludge method has not been established. Problems to be Solved by the Invention When eutrophicating substances such as BOD, ammonia compounds, nitrogen oxides, and phosphorus compounds in wastewater are efficiently removed using the batch activated sludge method, the following problems arise. be. (1) The order in which each eutrophic substance is removed is not clear. (2) The conditions for removing each eutrophication substance, i.e., aerobic and anaerobic conditions, are not specifically specified. (3) When each eutrophic substance in wastewater is removed one after another, the impact of the previous process on the subsequent process is not clear. For example, it has not been clarified how the amount of eutrophic substances remaining in the previous process, or the effects of treatment conditions such as ORP, dissolved oxygen concentration, and PH, on the treatment performance of the subsequent process. (4) A method for acclimating activated sludge that can remove eutrophic substances using the batch activated sludge method has not been clarified. In other words, the activated sludge used in the batch activated sludge method is often activated sludge in the continuous activated sludge method as a seed sludge. There is no established method to do so. Means for Solving the Problems The present invention relates, as a first invention, to a method for removing eutrophic substances from wastewater by a batch activated sludge method, and the features of the present invention are as follows. (1) The process from injecting wastewater into the biochemical reaction tank of the batch activated sludge treatment equipment to discharging the treated water from which eutrophic substances have been removed using activated sludge is a five-step treatment process. It's working. Note that, in the present invention, these five steps constitute one cycle. (2) At each stage of the treatment process, the oxidation-reduction potential (ORP) of the biochemical reactor can be controlled and managed, and each eutrophication substance can be efficiently removed. (3) Another effect of dividing one cycle into five treatment steps is that eutrophic substances in wastewater can be efficiently removed by the batch activated sludge method using activated sludge from continuous activated sludge treatment. can. Note that the biochemical reaction tank (hereinafter abbreviated as reaction tank) of the batch type activated sludge treatment equipment used in the present invention
In addition to air diffusers and mechanical stirring devices, ORP,
Sensors are installed to measure pH, dissolved oxygen concentration, temperature, etc., and these sensors are connected to a control device and recording device to control, measure, and monitor these inside the reaction tank.
Recording and management are becoming possible. It should be noted that the best ORP sensor used for activated sludge treatment is a composite electrode made of gold or gold alloy and silver chloride/silver, and other sensors can hardly be used. Next, the functions, actions, and characteristics of each step in one cycle of removing eutrophic substances according to the present invention will be explained. In the first step, a predetermined amount of wastewater containing eutrophic substances such as BOD, ammonia compounds, nitrogen oxides, and phosphorus compounds is injected into a reaction tank containing activated sludge while stirring. At this time, ORP of the reaction tank
gradually decreases, and eventually ORP reaches −200 to −
It drops to 300mV and becomes extremely anaerobic. When such an anaerobic environment is maintained for 30 minutes to 2 hours, phosphorus in the activated sludge is released into the waste water. For example, if the phosphorus compound content of the activated sludge before wastewater injection is 3 to 5% (as phosphorus), and the phosphorus compound content in the wastewater is 4 to 6 mg/(as phosphorus), the ORP will be - 200～-300mV
When maintained in an anaerobic state for 0.5 to 2 hours, the phosphorus compounds in the activated sludge decrease by 1 to 2 mg/g (as phosphorus), and the concentration of phosphorus compounds in the reaction tank decreases to 7 to 9 mg/g (as phosphorus).
mg/. In this way, the first stage is ORP
This is a process in which anaerobic stress is applied to activated sludge by lowering the phosphorus content, thereby releasing phosphorus compounds. In addition,
The ability to remove phosphorus compounds may vary depending on the ability of activated sludge to take up phosphorus compounds in the subsequent process or the concentration of phosphorus compounds in wastewater, so it may be desirable not to release large amounts of phosphorus compounds in this process. Yes, the ORP of the reaction tank is adjusted to suppress phosphorus release from activated sludge.
It is desirable to control the voltage to 100 to -300 mV, preferably -200 to -250 mV. The second stage is the process of removing BOD, adsorbing excess phosphorus compounds in the wastewater and the phosphorus compounds released by the activated sludge in the first stage into the activated sludge, and oxidizing ammonia compounds, organic amine compounds, etc. to nitrogen oxides. It is. Therefore, the second stage must be maintained in an aerobic environment, and the ORP suitable for performing all of the above actions is +100 to +120 mV or higher. If the ORP of the reaction tank is controlled to +100 to +120 mV or more and aeration is performed, 100 to 300 mg/kg of water in the waste water will be reduced after 2 to 4 hours.
BOD is below 10mg/, and 20-50mg/(as nitrogen) of ammonia nitrogen and Kjeldahl nitrogen are oxidized and reduced to below 1-2mg/, respectively, while nitrate and nitrite nitrogen are 20-50mg/(as nitrogen). 30
mg/ or more. In the first stage, the phosphorus compounds in the wastewater of the reaction tank were reduced from 7 to 9 mg/(as phosphorus) to 0.5 mg/
(as phosphorus) and the phosphorus concentration of activated sludge increases to 3-5%. In this case, in order to adsorb phosphorus compounds to the activated sludge, rather than simply changing the aerobic environment and anaerobic environment alternately to apply stress, the activated sludge is activated in the aerobic environment following the anaerobic environment as in the present invention. When sludge is subjected to decomposition of BOD components or oxidation of ammonia compounds, etc., the amount of phosphorus compounds taken into activated sludge increases significantly. This is because activated sludge releases phosphorus compounds in the anaerobic environment in the first stage, and is starved for phosphorus compounds in the aerobic environment, but due to decomposition of BOD components, nitrification reaction, etc.
Phosphorus compounds are required as a nutritional source, and it is thought that they take in large amounts of phosphorus compounds as a reaction. The third stage is a step in which nitric acid or nitrite nitrogen oxides are reduced to nitrogen gas and removed.
In order to reduce this nitrogen oxide with activated sludge,
Stop aeration and use mechanical agitation. At this time, a hydrogen donor is required, but this hydrogen donor can be used by newly injecting the used wastewater into the reaction tank, or by using an organic substance such as methanol, isopropyl alcohol, molasses, or rice bran. You can also do it. Since this third stage significantly affects the concentration of nitrogen compounds and phosphorus compounds in the treated water discharged in the fifth stage, it is important to control the ORP and nitrogen oxide concentration of the reaction tank. In other words, when a hydrogen donor is added and mechanical stirring is performed, the ORP of the reaction tank is 0 to -300m.
V. In particular, when ORP decreases to -250 to -300 mV, phosphorus compounds are released from the activated sludge, and the phosphorus compounds in the reaction tank become high. Another problem is that when such an anaerobic environment is used, anaerobic decomposition of activated sludge occurs, and the nitrogen concentration of ammonia compounds, organic amine compounds, etc. in the reaction tank also increases. Therefore, in some cases, it may be necessary to further remove phosphorus compounds, nitrogen compounds, etc. in the next step, making the treatment process very complicated. ORP management of the reaction tank is important to prevent these problems from occurring. In other words, there is a correlation between ORP, the concentration of nitrogen oxides remaining in the reaction tank, the release of phosphorus compounds from activated sludge, and anaerobic decomposition.
(as nitrogen), ORP is -200 ~
-300 mV, and in the ORP range of -50 to -150 mV, the nitrogen oxide concentration in the reaction tank is 0.5
It can be maintained at ~1.0 mg/(as nitrogen), and in an anaerobic environment of this level, release of phosphorus compounds from activated sludge and anaerobic decomposition of activated sludge can be suppressed. Therefore, in the third stage, it is necessary to control and manage the ORP of the reaction tank within the range of -50 to -150 mV. However, it is difficult to control and manage the ORP within this range with only mechanical stirring, and when the ORP drops below -50 to -150mV, the ORP control device aerates the reaction tank and raises the ORP to -50 to -150mV. maintained within the range for a predetermined period of time. In the fourth stage, aeration is performed to remove the excess hydrogen donor used in the third stage to maintain an aerobic environment. ORP in this fourth stage
The holding time varies depending on the type of hydrogen donor used and the regulatory value of the treated water discharged in the fifth stage. That is, if the nitrogen regulation value for the treated water to be discharged in the fifth stage is very strict, and if wastewater containing ammonia compounds and organic amine compounds is used as a hydrogen donor, it must be subjected to nitrification and denitrification before being discharged. In such cases, in the fifth stage, it is necessary to oxidize ammonia compounds, organic amine compounds, etc. in the wastewater to nitrogen oxides, and ORP
+50~+150mV, preferably +100~+1500m
It is necessary to maintain it at V. On the other hand, if the nitrogen regulation value of the treated water in the fifth stage is loose, or if a hydrogen donor that does not contain nitrogen is used, it is only necessary to remove the excess hydrogen donor or BOD component, so the ORP can be increased by +50 to +80 mV. Control and management is sufficient. In the fifth stage, aeration and mechanical stirring in the reaction tank are stopped to allow the activated sludge to settle, and approximately 80% or more of the supernatant water is discharged. In addition, if the nitrogen regulation value of the effluent water is strict, it is necessary to reduce the nitrogen oxides generated in the fourth stage.Addition of a hydrogen donor will complete the reduction in a short time; Even if the activated sludge is left to settle for a long time, the ORP will decrease and nitrogen oxides can be removed. Note that when the ORP inside the reaction tank becomes -200mV or less, the phosphorus compounds taken into the activated sludge are released, and the concentration of phosphorus compounds in the treated water discharged in the fifth stage may increase. Therefore, the ORP in the fifth stage must be controlled within this range with a limit of -50 to -150 mV, and the concentration of phosphorus compounds in the treated water can be reduced to 0.5 to 1.0 mg/(as phosphorus) or less. ORP control management in this fifth stage cannot be performed by aeration. That is, when aeration is performed, activated sludge does not settle and flows out into the treated water. For this reason, it is best to manage ORP based on the concentration of remaining nitrogen oxides.
In the fifth stage, maintaining the nitrogen oxides in the biochemical reactor at 0.5-1.0 mg/(as nitrogen) can maintain the ORP between -50 and -150 mV.
In order to maintain nitrogen oxides at 0.5 to 1.0 mg/(as nitrogen), the third stage ORP should be controlled to -50 to -150 mV. In addition, in the third stage, when wastewater containing organic amine compounds, such as sewage, is treated using an ammonia compound as a hydrogen donor, if the ORP of the reaction tank is +100 to +120 mV or more in the fourth stage, a nitrification reaction will occur. , forming nitrogen oxides. If this nitrogen oxide is not sufficiently removed in the fifth stage, it is carried into the first stage of the next cycle and the nitrogen oxide in the first stage of the next cycle is reduced to 0.5 mg/day.
If the above amount exists, the ORP may not be lowered sufficiently and the release of phosphorus compounds from the activated sludge process may not occur. To prevent this, it is necessary to control the ORP in the 4th stage to +50 to +80mV to suppress the production of nitrogen oxides, or to control the ORP in the 5th stage.
It is necessary to reduce the amount of nitrogen oxides generated in this step to 0.5mg/or less. Next, a method of acclimating activated sludge suitable for batch activated sludge treatment to activated sludge for continuous activated sludge treatment, which is the second invention of the present invention, will be described. Even if activated sludge from continuous activated sludge treatment such as urban sewage is used as activated sludge for the batch activated sludge method, the ability to immediately incorporate excessive amounts of phosphorus compounds in wastewater from wastewater into activated sludge is not maintained. Furthermore, the acclimatization method for providing the above-mentioned functions to activated sludge in continuous activated sludge treatment has not been clarified. However, when the five-step treatment method of the present invention described above is applied to activated sludge collected from continuous activated sludge treatment, eutrophic substances in wastewater can be removed in a short period of 2 to 5 days using the batch activated sludge method. can do. Example 1 An example of the method for acclimating activated sludge used in the batch activated sludge method of the present invention is shown. 20 samples of activated sludge mixture (activated sludge concentration approximately 2500mg/) were collected from the aeration tank of the activated sludge treatment equipment of a sewage treatment plant where urban sewage is continuously treated with activated sludge.
This was transferred to a biochemical reaction tank (effective volume: 30) of a batch-type activated sludge treatment experimental device, and the activated sludge was acclimatized. The acclimatization method is to stop aeration and mechanical agitation in the reaction tank, allow the activated sludge to settle, and discharge most of the supernatant water.
Over time, it is poured into urban sewage having the properties shown in Table 1, with mechanical stirring, until the total volume is 20. Mechanical stirring was further performed for about 30 minutes, and ORP in the reaction tank was controlled to -250 mV by aeration. Next, in the second step, mechanical stirring and aeration are performed to raise the ORP in the reaction tank to +100 to +120 mV.
It was maintained for 4 hours and 30 minutes. In the third stage, the aeration is stopped, mechanical agitation is performed, and approximately 5 of the municipal sewage from Table 1 is injected for 30 minutes or more, followed by mechanical agitation for approximately 2.5 hours.
In addition, when the ORP in the reaction tank becomes -130mV or less,
Aeration was controlled intermittently within this range. In the fourth step, aeration and mechanical stirring were performed for about 1 hour and 15 minutes so that ORP was +80 mV. In the fifth stage, the aeration and mechanical stirring were stopped, and the activated sludge was allowed to settle for about 45 minutes, after which the supernatant water was discharged for about 45 minutes, and after discharge, it was allowed to stand for about 15 minutes. One cycle from the first stage to the end of the fifth stage takes approximately 12 hours. 3 experiments of this cycle
After ~5 days, the quality of the effluent water (treated water) is as shown in Table 1.
As shown in Figure 2, the BOD was less than 10mg/, total nitrogen 4mg/, and total phosphorus 0.4mg/, and activated sludge that can remove eutrophic substances from urban sewage by the batch activated sludge method was achieved.

[Table] Example 2 Using the activated sludge acclimated in Example 1,
A cycle treatment experiment was conducted. The time allocation is as follows. In the first step, the urban sewage shown in Table 1 was injected for about an hour while mechanically stirring, and the total amount was about 1 hour.
It was set at 20. Immediately, a second stage of aeration was performed for about 2 hours, and the ORP was controlled to +140 mV. In the third stage, the aeration was stopped, only mechanical stirring was performed, and approximately 5 liters of municipal sewage was injected over a period of approximately 30 minutes, and the ORP was controlled to be -150 mV. This time is about 2 hours. If ORP falls below -150mV, perform aeration intermittently.
Performs ORP control management. The fourth stage is aeration for about 30 minutes.
Control and manage ORP to +80mV. Thereafter, aeration and mechanical stirring were stopped, the activated sludge was allowed to settle, and then the supernatant water was discharged for about 45 minutes. Furthermore, after leaving the water undisturbed for about 15 minutes,
Inject municipal sewage for the next cycle. In this way, the quality of the treated water treated three times a day is
BOD is about 3-5mg/, Kjeldahl nitrogen is about 5-5mg/
7 mg/, ammonia nitrogen 4-5 mg/, and total phosphorus 0.3 mg/. Note that both nitrate and nitrite nitrogen were 1 mg/or less. Effects of the Invention As explained above, in batch activated sludge treatment, the present invention injects wastewater into a reaction tank and uses activated sludge to remove BOD, ammonia compounds, nitrogen oxides,
By dividing the process from removing eutrophic substances such as phosphorus compounds to discharging wastewater into five stages, eutrophic substances can be efficiently removed. Furthermore, the present invention is an extremely effective method for acclimating activated sludge from continuous activated sludge treatment using a batch activated sludge treatment method.

Claims (1)

[Claims] 1. Wastewater containing eutrophic substances such as pollutants (BOD), ammonia compounds, nitrogen oxides, and phosphorus compounds as indicated by biochemical oxygen demand is processed by a batch activated sludge method. During treatment, one cycle of the process to remove eutrophic substances consists of the following five steps. The first step is to inject wastewater into a biochemical reaction tank containing activated sludge while mechanically stirring. death,
ORP is controlled and managed at an arbitrary ORP value in the range of -200 to -300 mV using a composite electrode made of gold alloy, silver chloride, and silver. The second step is to remove BOD and phosphorus compounds, and to oxidize ammonia compounds to nitrogen oxides. Aeration is performed, and the ORP is raised to +100 to +120 mV or more for a predetermined time using a composite electrode made of gold alloy, silver chloride, and silver. maintain. The third stage is the process of reducing the nitrogen oxides produced in the second stage to nitrogen gas. Mechanical stirring is performed, a predetermined amount of hydrogen donor is injected, and ORP is applied to a composite electrode made of gold alloy, silver chloride, and silver. to -50 to -150 mV, and perform ORP control in this range for a predetermined period of time. The fourth stage is aeration, with the main purpose of decomposing the excess hydrogen donor, and the ORP is set at +50 to +150 mV using a composite electrode made of gold alloy, silver chloride, and silver.
Perform control management using any value within the range of . The fifth step is a biological treatment method for wastewater, characterized in that aeration and mechanical stirring are stopped, activated sludge is allowed to settle, and about 80% or more of the supernatant is discharged.