JPS6094196A - Biological denitrification and dephosphorization process for organic waste water - Google Patents

Abstract

PURPOSE:To simplify a treating system and to reduce consumption of chemical agents by treating org. waste water contg. ammonical nitrogenor org. nitrogen compds. and phosphorus compds. by biological denitrification process alone. CONSTITUTION:Discharged water from a reaeration stage 10 is flowed into a second sludge separation stage 12, and is separated into supernatant liquid and settled activated sludge. The supernatant liquid flows out of a treating liquid pipe 15, and a part of the activated sludge separated in the second sludge separating stage 12 is discharged to the outside of the system as excess sludge 14, and residual portion is introduced into a second anaerobic stage 17 through a return pipe 11. Since the excess sludge 8 can absorb and contain a large amt. of P in the aeration stage, P compds. remaining in the supernatant liquid in the first sludge separating stage 5 is removed by the excess sludge and is discharged to the outside of the system to reduce the P content in the treated water discharged from the treating liquid pipe 15 to less than the content of P in the supernatant liquid of the first sludge separation stage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for biological denitrification of organic wastewater.

A conventional method for biologically denitrifying organic wastewater containing a large amount of nitrogen compounds such as ammonia nitrogen or organic nitrogen is shown in FIG.

In FIG. 1, wastewater 1 is introduced into a nitrogen stage 2,
It is mixed with the nitrification mixed liquid returned from the nitrification process 3 through the circulating liquid pipe 4 and the return sludge returned from the first sludge separation process 5 through the return pipe 6. No, -N or No contained in the nitrification mixture in the nitrogen step 2,
-N is reduced to N2 gas by the biological reduction action of denitrifying bacteria in activated sludge using the BOD source contained in the raw wastewater as a hydrogen donor.

Theory - Nitrogen The effluent from the nitrogen process 2 contains N contained in the raw wastewater.
Since H and -N are contained without undergoing any biological action in the nitrogen process, they are introduced into the nitrification process B, and while supplying oxygen through aeration, NO is produced by the action of nitrifying bacteria in the activated sludge. □ Oxidize to -N or No, -N.

When NH4-N is oxidized to NO□-N or No, -NK, hydrogen ions are released into the mixed solution, which lowers the pH of the mixed solution and impedes the activity of nitrifying bacteria. An alkaline agent such as slaked lime or caustic soda is added to the nitrification step 6 to adjust the pH of the mixture to a range suitable for the activity of nitrifying bacteria. A part of the effluent from the nitrification process 3 is returned to the first nitrogen process 2 through the circulating liquid pipe 4, and the remainder is introduced into the first sludge separation process 5. The effluent from the nitrification process B that has flowed into the first sludge separation process 5 is separated into a supernatant liquid and settled activated sludge in the first sludge separation process 5.

A part of the activated sludge separated by sedimentation in the first sludge separation step 5 is discharged outside the system as surplus sludge 8, and the remainder is returned to the second nitrogen step 2 through a return pipe 6.

In the supernatant liquid of the first sludge separation step 5, the portion of N'02-N or NO,-14 generated in the nitrification step 5 that has been reduced to N2 gas remains.

The supernatant liquid of the first sludge separation step 5 flows into the second denitrification step 9 and is mixed with the return sludge returned through the return pipe 11. In the second denitrification diameter 9, the NO□-N or No, -N remaining and contained in the supernatant liquid of the first sludge separation process is supplied with methanol or ethanol, etc. supplied from the hydrogen donor supply device 13 as a hydrogen donor. As a result of the biological reduction action of denitrifying bacteria in activated sludge, N and gas are reduced.

The effluent from the second denitrification step, which has undergone the action of reducing the residual No. -N or No. These hydrogen donors are aerobically treated with activated sludge in the reaeration step 10 and removed. The effluent from the reaeration process flows into the second sludge separation process 12 and is separated into a supernatant liquid and settled activated sludge. The supernatant liquid is treated liquid 915.
A part of the activated sludge that flows out and is sedimented and separated in the second sludge separation step 12 is discharged outside the system as surplus sludge 14, and the remainder is returned to the second denitrification step 9 through the return pipe 11.

As described above, when wastewater is treated in the first illustrated example, nitrogen compounds and organic substances in the wastewater can be efficiently treated, but the removal rate of phosphorus compounds in the wastewater is low. Usually the first
Phosphorus compounds remaining in the treated water in the illustrated example are removed by a coagulation-sedimentation method as a post-treatment. The coagulation-sedimentation method requires a large amount of chemicals such as flocculants, and the generated surplus sludge has poor dewatering properties, which may adversely affect the surplus sludge treatment process.

The purpose of the present invention is to eliminate the above-mentioned drawbacks by simultaneously treating and removing phosphorus compounds in wastewater during the biological internal membrane nitrogen treatment process of wastewater. Instead of treating organic matter, IT compounds, and phosphorus compounds in wastewater using a combination of treatments, we now also treat phosphorus compounds at the same time in the biological membrane nitrogen treatment process, simplifying the treatment system and making it even more effective compared to conventional methods. This is a method that reduces the amount of chemicals required for phosphorus removal to just a sliver, or eliminates the use of chemicals.

To increase the phosphorus uptake capacity of activated sludge, first, under absolute anaerobic conditions (dissolved sulfur, DO and NO).

-N, N03-N is not present), the phosphorus in the activated sludge is released into the liquid as soluble phosphorus. (2
) Next, the present inventors came up with the idea of applying this method, as it has been experimentally found that activated sludge is placed under aerobic conditions and allowed to stagnate, resulting in excessive intake of phosphorus. The biological denitrification membrane phosphorus method of the present invention was developed based on the above.

Since the conventional method shown in FIG. 1 does not have an absolute anaerobic tank, excessive phosphorus uptake in activated sludge is less likely to occur, and phosphorus remains in the treated water.

That is, the gist of the present invention is to introduce organic wastewater containing nitrogen compounds such as ammonia nitrogen or organic nitrogen and phosphorus compounds into the first anaerobic process, mix it with return sludge returned from the first sludge separation process, The first anaerobic process effluent is introduced into the second nitrogen process and mixed with the circulating liquid from the nitrification process,
He introduced the nitrification process effluent into the nitrification process. A part of the nitrification process effluent was returned to the nitrification process as circulating fluid, and the remainder was introduced into the first sludge separation process, forming the supernatant liquid. The first process involves solid-liquid separation into settled activated sludge, a part of the separated activated sludge is extracted from the system as surplus sludge, and the remainder is returned to the first anaerobic process as return sludge, and the first sludge separation process supernatant liquid. is introduced into the second denitrification process and mixed with the second anaerobic process effluent, the first anaerobic process effluent is introduced into the reaeration process, and the reaeration process effluent is introduced into the second sludge separation process and supernatant. The solid-liquid is separated into liquid and settled activated sludge, and the supernatant liquid is discharged outside the system as treated water. A part of the separated activated sludge is drawn out of the system as surplus sludge, and the remainder is introduced into the second anaerobic tank. , from the second step in which the second anaerobic tank effluent is returned as return sludge to the second denitrification step. The present invention provides a biological denitrification and dephosphorization method for organic wastewater characterized by the following.

The method of the present invention for biologically dephosphorizing and denitrifying organic wastewater containing nitrogen compounds such as ammonia nitrogen or organic nitrogen and phosphorus compounds is shown in FIGS. 2 and 6.

In FIG. 2, wastewater 1 is introduced into a first anaerobic step 16,
The first sludge separation step 5 is mixed with the return sludge that is returned through the return pipe 6. In the first anaerobic process, No, -N or No, -N contained in the returned sludge is reduced by the biological reduction action of denitrifying bacteria in the activated sludge, using the BOD source contained in the wastewater as a hydrogen donor. N is reduced to gas, and NOx-N no longer exists, and dissolved oxygen (D
It becomes an absolute anaerobic state where o) also does not exist. When the mixed solution of raw water and returned sludge is allowed to remain in the first anaerobic step even after the state becomes absolutely anaerobic, the phosphorus compounds contained in the activated sludge are released into the solution as soluble phosphorus. The effluent from the first anaerobic process 16, in which the concentration of phosphorus in the liquid has increased due to the release of phosphorus from the activated sludge, flows into the nitrogen process 2 together with the nitrification mixture returned from the nitrification process 3 through the circulating liquid pipe 4. mixed. Theory - No2-N or No, -N contained in the nitrification mixture in the nitrogen step 2. Denitrification bacteria in the activated sludge are activated using the BOD source contained in the effluent of the first anaerobic step as a hydrogen donor. It is reduced to N2 gas by biological reduction action. In the effluent of the second theory nitrogen step 2, NH and -N contained in the raw wastewater are contained without being subjected to biological effects in the second theory nitrogen step, and the phosphorus compounds in the raw wastewater are Since the activated sludge contains soluble phosphorus in the first anaerobic step, it is introduced into the nitrification step 3, and while supplying oxygen through aeration, NO, -N, or While being oxidized to No. 3 -N, the activated sludge takes in a larger amount of phosphorus compounds in the liquid than the activated sludge of the first illustrated example and removes phosphorus from the liquid. In the nitrification process 3, a dialkali agent is added to the pH adjuster 7 to adjust the pH of the mixed liquid.
Adjust H to a range suitable for the activity of nitrifying bacteria. Nitrification process 3
A part of the effluent is passed through the circulating liquid pipe 4 to the nitrogen process 2.
and the remainder is introduced into the first sludge separation step 5.

The effluent from the nitrification process B that entered the first sludge separation process 5 is
In the first sludge separation step 5, the sludge is separated into a supernatant liquid and activated sludge that settles. A portion of the activated sludge separated by sedimentation in the first sludge separation step 5 is discharged outside the system as surplus sludge 8, and the remainder is returned to the first anaerobic step 16 through the return pipe 6. Since the surplus sludge 8 takes in a large amount of phosphorus during the nitrification process and contains it, the phosphorus compounds contained in the raw wastewater are removed from the surplus sludge and discharged outside the system, so the first sludge separation process 5 The supernatant water has phosphorus compounds removed to a large extent.

In addition, when activated sludge and supernatant water are solid-liquid separated in the sludge separation process, when the activated sludge separated from the supernatant liquid is exposed to anaerobic conditions, the phosphorus in the activated sludge is released into the liquid, and the phosphorus in the supernatant water It will increase the concentration. The inflow water to the sludge separation process 5 of the present invention necessarily contains NO and -N generated in the nitrification process 3.
The activated sludge that has been separated into solid and liquid in the sludge separation step 5 also contains NO, -N or No.
3-N is contained. No, -N or N 03-
When N coexists with activated sludge, it is difficult to become absolutely anaerobic, and phosphorus release from activated sludge can be suppressed. It is possible to suppress the decline due to phosphorus release.

Up to sludge separation step 5, most of the phosphorus compounds and nitrogen compounds contained in the raw wastewater are removed, but nitrogen compounds (N
o2-N or No, -N) and phosphorus compounds remain, so these residues are removed in the next step.

That is, the supernatant liquid from the first sludge separation process 5 flows into the second denitrification process 9 and is mixed with the return sludge returned through the return pipe 11. No, -N or No3-N remaining and contained in the overlay liquid flowing in the second anaerobic process 9 is activated sludge using methanol, ethanol, etc. supplied from the hydrogen donor supply device 13 as a hydrogen donor. It is reduced to I4□ residue by the biological reduction action of the denitrifying bacteria inside. However, as will be described later, the amount of hydrogen donor added to the second anaerobic step is the same as No2-N or N in the second decarboxylation step 9.
Second arm nitrogen step 2 if sufficient for o3-N reduction
It is not necessary to add a hydrogen donor to.

The effluent from the second denitrification step 9 flows into the reaeration step 1°,
Hydrogen donors such as methanol or ethanol remaining in the second anaerobic step are removed by aerobic activated sludge treatment in the reaeration step 10, and are removed in the first sludge separation step 5.
The phosphorus compounds remaining in the supernatant liquid and the soluble phosphorus released from the activated sludge in the second anaerobic process 17 described below flow into the reaeration process 10 via the second denitrification process 9, Phosphorus is removed from the liquid by the activated sludge in the first illustrated example ingesting a large amount of phosphorus compounds in the liquid. The effluent from the reaeration process 10 flows into the second sludge separation process 12 and is separated into a supernatant liquid and settled activated sludge. The supernatant liquid flows out from the treated liquid pipe 15, and a part of the activated sludge that has been sedimented and separated in the second sludge separation process 12 is discharged to the outside as surplus sludge 14, and the remainder passes through the return pipe 11 to the second anaerobic process 17. will be introduced in Since the surplus sludge 8 takes in a large amount of phosphorus during the re-aeration process and contains it, the phosphorus compounds that remained and were not contained in the supernatant liquid of the first sludge separation process 5 are removed from the surplus sludge and released outside the system. The processing liquid pipe 1
5) The amount of phosphorus in the treated water flowing back is further reduced in the supernatant water of the first sludge separation process. The surplus sludge that has flowed into the second anaerobic process 17 is kept in an anaerobic state and releases phosphorus in the activated sludge. Since phosphorus is released more easily when BOD is present, the second anaerobic step 17 is supplied with a BOD source as well as the hydrogen donor supply device 16 . At that time B
As the OD source, it is preferable to select methanol, ethanol, or the like, which is effective as a hydrogen donor during denitrification in the second anaerobic step 9.

The mixed liquid from which phosphorus in the activated sludge has been released in the second anaerobic process is returned to the second anaerobic process.

According to the present invention, as shown in the second illustrated example, nitrification, denitrification, and dephosphorization are performed simultaneously in the first step,
In order to improve the nitrification effect, it is necessary to maintain nitrifying bacteria in the system, so SRT (sludge gold) is added to the nitrifying bacteria was
It is necessary to set it to a value greater than or equal to the value at which h out does not occur. Washout (antigen) as used herein means that when excess sludge is removed at a rate faster than the growth rate of nitrifying bacteria, the nitrifying bacteria are eliminated from the system. SRT is limited, that is, setting the withdrawal rate of excess sludge requires the amount of excess sludge 8 to be below a certain value, and since there is an upper limit to the phosphorus content in excess sludge, the phosphorus content in the first step is The amount removed is 1lt due to SRT K for retaining nitrifying bacteria in the system.
lJ is limited. However, the second step mainly aims at denitrification and large removal and does not require nitrification treatment, so there is no need to perform SRT control to retain nitrifying bacteria as in the first step.

Therefore, the amount of BOD added to the second step by the hydrogen donor supply device 13 is increased or decreased, the ratio of BOD t loaded to the second step and the amount of P is made appropriate for biological dephosphorization, and the amount of BOD added to the second step is adjusted to be appropriate for biological dephosphorization. Since it is possible to supply a sufficient amount of OD for the treatment, it is possible to sufficiently treat phosphorus compounds, No2-N and No,-N contained in the effluent water from the first step, and obtain good treated water quality. can.

Misfire 8A can also be performed by the method shown in FIG. The difference from the example shown in Figure 2 is that the first sludge separation step 5
The effluent water and the returned sludge from the second sludge separation process 12 are made to flow into the second anaerobic process 17, and the effluent water from the second anaerobic process is introduced into the second denitrification process.

Sludge separation steps 5 and 1 in the second illustrated example and the third illustrated example
For 2, a device for separating treated water and activated sludge, such as a gravity settling tank or a pressurized flotation tank, can be used.

[Brief explanation of the drawing]

Figure 1 shows the general flow of the conventional biological membrane nitrogenization method for organic wastewater, and Figures 2 and 3 show the biological dephosphorization and denitrification method for organic wastewater according to the method of the present invention. 2 shows a schematic flow of one row and another row; Sub-agents 1) Meifuku agent Ryo Hagiwara -

Claims (1)

[Claims] 1. Organic wastewater containing nitrogen compounds such as ammonia nitrogen or organic nitrogen and phosphorus compounds is introduced into the first anaerobic process, mixed with the return sludge returned from the first sludge separation process, and then removed from the first anaerobic process outflow. Water is introduced into the nitrification process and mixed with the circulating fluid from the nitrification process, and after the effluent water from the nitrification process is introduced into the nitrification process, a portion of the nitrification process effluent is used as the circulating fluid. At the same time as returning it to the process, the remaining sludge is introduced into the first sludge separation process, where it undergoes solid-liquid separation into supernatant liquid and settled activated sludge, and a portion of the separated activated sludge is pulled out of the system as surplus sludge, and the remaining sludge is removed. The supernatant liquid from the first process and the first sludge separation process, which is returned to the first anaerobic process as return sludge, is introduced into the second denitrification process, mixed with the second anaerobic process effluent, and the first anaerobic process effluent is recycled. The effluent from the reaeration process is introduced into the second sludge separation process, where it is solid-liquid separated into supernatant liquid and settled activated sludge. The supernatant liquid is discharged outside the system as treated water, and the separated activated sludge is A part of the sludge is drawn out of the system as surplus sludge, the residue is introduced into the second anaerobic tank, and the water flowing out of the second anaerobic tank is returned as return sludge to the second denitrification process. A biological dephosphorization method for organic wastewater, characterized by injecting the body into a second anaerobic step and a second denitrification step, or only into the second anaerobic step.