JPS6121790A - Treatment of sewage - Google Patents

Abstract

PURPOSE:To enhance the effect of biological treatment, by removing ammoniacal nitrogen from sewage containing a BOD component, a nitrogen component and a phosphorus component before performing boilogical treatment including anaerobic treatment and aerobic treatment. CONSTITUTION:Biological treatment including anaerobic treatment and aerobic treatment is performed after ammoniacal nitrogen is removed from aewage containing a BOD component, a nitrogen component and a phosphorus component. for example, the removal of ammonical nitrogen is performed by an ammonia stripping method. That is, raw sewage 1, to which an alkali agent 9 was added, is introduced into a gas-liquid contact reactor 10 where sewage is contacted with gas 11 and ammonia in sewage is volatilized into the gas as ammonia gas. The sewage 13, from which ammonia was removed, is introduced into an anaerobic tank 4 along with the return sludge 3 obtained from a sedimentation basin 2 to receive anaerobic treatment and the resulting sludge mixed liquid receives aerobic treatment in an aerobic tank 5 to be introduced into the sedimentation basin 2 where solid-liquid separation is performed to obtain separated sludge and separated water 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for biologically treating wastewater containing BOD components, ammonia nitrogen components and phosphorus components.

[Conventional technology]

Conventionally, the activated sludge method has been widely used to treat organic wastewater containing BOD components, nitrogen components, phosphorus components, etc., and the standard activated sludge method mainly treats BOD components. It is possible. In this method, the sludge absorbs pollutants in the wastewater and multiplies, so the nitrogen and phosphorus components used for bacterial cell synthesis are also removed, but the amount removed is compared to the amount of BOD removed. few. Therefore, when standard activated sludge treatment is applied to wastewater such as sewage or human waste, nitrogen and phosphorus components remain at relatively high concentrations. Nitrogen and phosphorus are the causative agents of eutrophication in closed water bodies, and their removal is desired, but standard activated sludge methods have not been able to adequately address this problem.

Recently, various methods for solving such problems have been studied. Figure 3 shows the BOD component.

BOD for wastewater containing nitrogen and phosphorus components
, shows an example of a method for biologically removing nitrogen and phosphorus. In this method, raw sewage 1 is introduced into an anaerobic tank 4 together with return sludge 3, which is a part of the sludge obtained in a settling tank 2, and after anaerobic treatment, the sludge mixture is transferred to an aerobic tank (aeration tank) 5. In this method, the water is subjected to aerobic treatment and passed through a settling tank 2 to obtain treated water 6. In this method, when sludge is treated anaerobically in the presence of organic matter, the sludge releases its phosphorus, and then treated aerobically,
Phosphorus is removed by utilizing the phenomenon that sludge is released and more than 90% of phosphorus is taken into the body. By this method, the phosphorus in the raw sewage is finally concentrated in the sludge, and the phosphorus is removed. Removal from sewage is completed by separating, removing, treating, and disposing of sludge.

In addition, in the anaerobic tank 4, denitrifying bacteria, which are anaerobic bacteria, are present, so if nitrite nitrogen and nitrate nitrogen produced as a result of nitrification treatment are introduced, the BOD component in the raw wastewater 1 can be used as an organic carbon source. A biological denitrification reaction occurs. In the aeration tank 5, aerobic biological treatment is performed to keep the BOD sludge load low, thereby performing BOD removal and nitrification. Although not shown in FIG. 3, by circulating a portion of the sludge mixture in the aerobic tank 5 or a portion of the treated water 6 to the anaerobic tank 4, nitrite nitrogen generated in the nitrification process, Nitrate nitrogen can be introduced into the anaerobic tank 4 to perform denitrification treatment.

Thus, by using this method, biologically B.
OD removal, denitrification and dephosphorization treatments are possible.

[Problem that the invention seeks to solve]

However, from the outside, this method is a method in which BOD removal and denitrification and dephosphorization are all performed by the action of living organisms. Therefore, the treatment performance of this method is affected by the toxicity of ammonia nitrogen in the raw wastewater, and when the ammonia nitrogen concentration is high, the inhibitory effect is significant. In addition, in this method, the raw sewage 1 is subjected to anaerobic treatment in the anaerobic tank 4, so cyanmoniac nitrogen is produced by decomposition of protein components in the raw sewage, and a synergistic effect between the sewage and the ammonia nitrogen in the raw sewage occurs. There is also the problem that the biological activity of anaerobic treatment and aerobic treatment is inhibited by this. Also, nitrite nitrogen produced as a result of nitrification.

Another problem is that when nitrate nitrogen is introduced at a high concentration into the anaerobic treatment process, the anaerobic reaction among the biological dephosphorization reactions is inhibited.

Figure 4 shows BOD removal and denitrification using conventional technology.

This figure shows another example of a biological treatment method for dephosphorization treatment. This method differs from the conventional method shown in FIG. 3 in that a denitrification tank 7 is provided and a circulation path 8 for the sludge mixture from the aerobic tank 5 to the denitrification tank 7 is provided. That is, in this method, an anaerobic tank 4 that performs an anaerobic reaction for dephosphorization and a denitrification tank 7 that performs an anaerobic reaction for denitrification are separated.

According to method B, nitrite nitrogen and nitrate nitrogen generated by nitrification in the aerobic tank 5 are not introduced into the anaerobic tank 4, and the anaerobic reaction of the biological dephosphorization reaction is eliminated. can be prevented from being inhibited by nitrite nitrogen and nitrate nitrogen.

However, even in this method, ammonia derived from ammonia nitrogen or protein components in the raw wastewater;
Phenomena such as outages cannot be avoided.

The present invention has been made in view of the above circumstances, and its purpose is to improve the treatment effect by removing ammonia nitrogen in advance and then performing biological Hiko wastewater treatment. It is something.

[Means for solving problems]

That is, in the present invention, wastewater containing BOD components, nitrogen components, and phosphorus components is subjected to physicochemical pretreatment such as ammonia stripping method, zeolite adsorption method, ion exchange method, discontinuous point chlorination method, etc. This is a wastewater treatment method that effectively performs biological treatment including anaerobic treatment and aerobic treatment after removing ammonia nitrogen to eliminate the influence of ammonia nitrogen on biological reactions.

〔Example〕

The method of the present invention will be explained below with reference to illustrative examples.

FIG. 1 is a flow sheet showing one embodiment of the sewage treatment method according to the present invention. In this method, ammonia nitrogen is removed by an ammonia stripping method. That is, after adding the alkaline agent 9 to the raw sewage 1, the raw sewage 1 is introduced into the gas-liquid contact reactor 10, where the gas 11 and the sewage are brought into contact with each other, and the ammonia in the sewage is volatilized into the gas as ammonia gas. Then, a gas 12 containing ammonia and waste water 13 from which ammonia has been removed are obtained. In this step, slaked lime, aqueous soda, etc. can be used as the alkali agent 9. Further, the amount added varies depending on the properties of the raw sewage, such as the ammonia nitrogen concentration, acidity, or desired ammonia nitrogen removal rate.

For example, to obtain a removal rate of 90% or more, add an alkali agent so that the pH becomes 11 or more, and to obtain a removal rate of about 50%, add an alkali agent to make the PI (about 9 to 10). Good. As the gas 1), air, water vapor, etc. can be used.

Next, the gas 12 containing ammonia is further processed as necessary. On the other hand, sewage from which ammonia was removed 1
Regarding 3, the sludge mixture is introduced into the anaerobic tank 4 together with the returned sludge 3 obtained from the settling tank 2 for anaerobic treatment, and then the sludge mixture is subjected to aerobic treatment in the aerobic tank 5, and then the sludge mixture is sedimented. Pond 2
The solid and liquid are separated into separated sludge and separated water (treated water 6).
and get.

According to this method, the ammonia nitrogen concentration in the raw wastewater is reduced to the desired concentration before introducing it into the biological treatment process, and the biological treatment reaction rate is prevented from decreasing due to ammonia nitrogen. If you make effective use of it, you can achieve. That is, since the concentration of nitrogen introduced into the biological treatment process decreases, the concentration of nitrite nitrogen and nitrate nitrogen produced by the nitrification reaction in the aerobic tank 5 decreases, which causes anaerobic treatment. The inhibitory effect on the biological dephosphorization anaerobic reaction when it is circulated back to the tank 4 can also be reduced. Furthermore, in general, the ammonia nitrogen removal reaction rate per unit volume of the reaction tank is higher in the physicochemical treatment method as in the pretreatment step shown in FIG. 1 than in the biological treatment method. Therefore, by performing such pre-processing, the entire processing apparatus can be interconnected.

In the embodiment shown in Fig. 1, a stripping method was used in the ammonia removal process, but it is also possible to use a zeolite adsorption treatment method, an ion exchange treatment method, or a discontinuous point chlorine treatment method instead. .

In addition, in the biological treatment process part of the embodiment shown in FIG.
It is also possible to circulate and return the sludge mixture from the aerobic tank 5 to the anaerobic tank 4, or to circulate and return a portion of the treated water 6 to the anaerobic tank 4.

FIG. 2 is a flow sheet showing another embodiment of the sewage treatment method according to the present invention. This method is similar to the embodiment shown in FIG. 1 in that raw wastewater 1 is subjected to a stripping treatment to obtain wastewater 13 from which ammonia has been removed. In this embodiment, the sewage from which ammonia has been removed is introduced into the anaerobic tank 4 together with the return sludge 3 obtained from the settling tank 2 for anaerobic treatment, and then the sludge mixture is introduced into the denitrification tank 7, which is another anaerobic tank. .

Then, the sludge mixture is transferred from the aerobic tank 5 to I! 51! The sludge mixture is circulated and returned to the nitrogen tank 7 through the circulation path 8 1, and both the sludge mixture and the sludge mixture from the anaerobic tank 4 are subjected to denitrification treatment, and then the sludge mixture is subjected to aerobic treatment in the aerobic tank 5. Next, the sludge mixture is subjected to solid-liquid separation in the settling tank 2 to obtain treated water 6.

According to this method, it is possible to prevent the synergistic effect of reducing biological treatment efficiency due to the ammonia nitrogen in the raw wastewater and the ammonia nitrogen generated during the process in which the protein nitrogen in the raw wastewater undergoes anaerobic biological treatment. can. This point is similar to the case of the embodiment shown in FIG.

In the embodiment shown in FIG. 2, the fluornitrate nitrogen and nitrate nitrogen returned from the aerobic tank 5 do not enter the anaerobic tank 4, which is the reservoir for the biological dephosphorization anaerobic reaction, so nitrite is returned to the denitrification tank 7. Even if the concentrations of ammonia nitrogen and nitrate nitrogen are high, good phosphorus removal performance can be obtained, and it is possible to reduce the ammonia nitrogen removal rate in the pretreatment step.

Similar to the embodiment shown in FIG. 1, a zeolite adsorption treatment method or an ion exchange treatment method can also be used as a method for removing anthonia nitrogen.

[Experiment example]

Next, examples in which experiments were conducted based on the present invention will be described. The apparatus used in the method of the present invention is based on FIGS. 1 and 2, and the apparatus used in the comparative method is the one shown in FIG.
It is based on FIG.

As raw sewage 1, synthetic wastewater was used, and the treatment amount was 0.2
m"/day. The effective capacity of the device based on Figure 3 is 0.2 m" for the anaerobic tank 4, 0.6 m3 for the aerobic tank 5,
In the apparatus based on FIG. 4, an anaerobic tank 4 and a denitrification tank 7
were each 0.1 m" *The aerobic tank 5 was 0.6 m". The effective capacity of the biological treatment reaction tank of the apparatus based on FIGS. 1 and 2 was set to be 1710 times the effective capacity of the reaction tank in FIGS. 3 and 4, respectively. Based on FIG. 3, in the conventional method and the apparatus according to the present invention method based on FIG.
Based on FIG. 4, the circulating return flow rate from the aerobic tank 5 to the denitrification tank 7 was set to 0.4 m/day.

In either case, the flow rate of the return sludge 3 is 0.2fn37
It was a day. In the method of the present invention based on FIGS. 1 and 2, a 40% strength soda aqueous solution is added to the raw sewage 1 to adjust the pH to 11, and a volume of air 1200 times the volume of the raw sewage 1 is supplied through an aeration tube. Ammonia nitrogen removal treatment was performed by blowing through the tank. In each biological treatment device, the anaerobic tank 4 and denitrification tank 7 are stirred by a stirrer, and the aerobic tank 5 is Do 2 m? Aeration was carried out through an aeration pipe so that the air pressure was 0.7 or higher.

The water quality analysis results obtained in this experiment are shown in Table 1.The water quality of the water treated by the method of the present invention was as good as that of the water treated by the conventional method. It was found that the BOD removal amount, total nitrogen removal amount, and phosphorus removal amount per unit effective capacity were higher than those of the conventional method, and the biological treatment activity was effectively exhibited. [Effects of the Invention] The present invention According to the study, since ammonia nitrogen is removed in advance before biological treatment, BOD removal, denitrification, and
Biological treatment for simultaneous dephosphorization can be performed effectively, especially for wastewater where ammonia nitrogen concentration and protein nitrogen concentration are higher than BOD concentration and phosphorus concentration. is remarkable.

4. Brief explanation of the figures FIG. 1 is a flow sheet diagram showing one example of the wastewater treatment method according to the present invention, FIG. 2 is a flow sheet diagram showing another example of the method of the present invention, and FIGS. FIG. 4 is a flow sheet diagram showing a conventional wastewater treatment method.

1... Raw sewage, 2... Sedimentation tank, 3... Returned sludge,
4... Anaerobic tank, 5... Aerobic tank, 6... Treated water, 7
... denitrification tank, 8 ... circulation path, 9 ... alkali agent, 10 ... gas-liquid contact reactor, 11 ... gas, 12.
...Gas containing ammonia, 13...Sewage treated to remove ammonia.

Claims (1)

[Claims] A method for treating wastewater, which involves removing ammonia nitrogen from wastewater containing BOD components, nitrogen components, and phosphorus components, and then performing biological treatment including anaerobic treatment and aerobic treatment.