JPS5992095A - Biological nitrification-denitrification of waste water - Google Patents

Abstract

PURPOSE:To curtail the amount of an additive such as methanol, while making a denitrification tank small size, by nitrifying and denitrifying waste water in a high MLSS step under a high load, and nitrifying and denitrifying separated water from the step of solid-liquid separation in a low MLSS step. CONSTITUTION:Waste water 1 flows together with returned sludge 2 and a circulatory digested liquid 3 into the first denitrification step 4 under an anaerobic condition. After NOX in the circulatory digested liquid 3 is denitrified by BOD components in the waste water 1, the mixed liquid flows into the first nitrification step 5 under an aerobic condition, to nitrify NH3 in the waste water 1 into NOX. A part of the mixed liquid is then circulated to the first denitrification step 4, while the remainder is let flow into the second denitrification step 6 to denitrify NOX. Separated water 12 in the first solid-liquid separation step 8 flows into the third denitrification step 9 to denitrify NOX formed by nitrification in the second nitrification step 7. The denitrified mixed liquid flows into a reaeration step 10 to remove remaining BOD, and then sludge is separated by solid-liquid separation in the second solid-liquid separation step 11.

Description

[Detailed description of the invention] The present invention relates to a biological nitrification-denitrification method for wastewater.

The biological nitrification and denitrification method of wastewater is a method that uses nitrogen (hereinafter referred to as NH) in wastewater.
3) by nitrifying bacteria under aerobic conditions.
After being nitrified to N02 and/or N03), NO is reduced and decomposed to N2 gas by denitrifying bacteria under anaerobic conditions.

When denitrifying NO, substances that act as reducing agents are used by denitrifying bacteria, but the reducing agents include BOD components contained in wastewater, carbonaceous organic compounds such as methanol and ethanol, and even carbonaceous organic compounds such as methanol and ethanol. There are intracellular substances possessed by activated sludge microorganisms themselves. Denitrification using an externally added reducing agent such as methanol or ethanol is called exogenous respiration denitrification, and although the denitrification rate is high, denitrification costs are high because valuable industrial chemicals are used. The disadvantage is that it is expensive.

On the other hand, denitrification that uses activated sludge microorganisms themselves as reducing agents is called endogenous respiration denitrification. This type of denitrification is economical because it does not require the addition of a reducing agent from the outside, and because sludge is reduced through endogenous respiration, the amount of excess sludge generated is small and is advantageous from a sludge treatment perspective. Since the speed is much lower than that of the exogenous respiration type, the denitrification tank is correspondingly larger, and NH3 is eluted from the activated sludge during endogenous respiration, resulting in a lower nitrogen removal rate.
There are few examples of adoption.

The present invention was conceived to take advantage of the advantages of endogenous respiration type denitrification described in -E and to compensate for its disadvantages. Nitrification and denitrification process and solid-liquid separation process using sludge
The high MLSS process consisting of 1) is followed by a nitrification denitrification process using low concentration activated sludge and a solid-liquid separation process (IN).
), the wastewater is subjected to nitrification and deaeration treatment at high load in the high MLS S process,
The separated water from the solid-liquid separation step (summer) is converted into the low MLSS
This is a biological nitrification and denitrification method for wastewater, which is characterized by a nitrification and denitrification process in the process.

Next, the circumstances that led to the completion of the present invention will be explained.

The inventors have proposed a method to actively utilize endogenous respiration denitrification, which has a denitrification rate of only 1 to 1/10 of the denitrification rate of exogenous respiration denitrification. In order to achieve the same level as exogenous respiration type denitrification, the MLSS concentration in the denitrification tank should be increased from 2 to 2.
A nitrification and denitrification treatment test was conducted under extremely high concentration conditions of 20,000 q and 4 times the concentration.

As a result, although the amount of denitrification per unit volume was able to increase, the NH3 concentration eluted from sludge during endogenous respiration type denitrification increases in proportion to the sludge concentration and denitrification time, resulting in a high sludge concentration. Now, we have found the drawback that the NH3-N concentration in the denitrified water increases.

Therefore, we set up a tank to nitrify and denitrify the NH3 in the denitrification treated water again.As with the previous stage nitrification and denitrification tank, we performed nitrification and denitrification at a high concentration. , is larger than the NO produced by nitrification of N1-13 eluted in the previous stage denitrification tank, and these NO,
During denitrification, NH3 is eluted again, and N■
13 was difficult to reduce.

For this reason, the activated sludge concentration in the second nitrification and denitrification process was lowered to 500,044 in the previous stage (first stage) 4 for nitrification.

After denitrification treatment, the amount of NO produced by nitrification of the nitrogen in activated sludge during the nitrification process decreased, and the amount of NO generated during the denitrification process decreased.
, NH3 is still eluted even in the denitrification tank due to low load.
It was found that -N could be kept low at 9 degrees and good treated water could be obtained.

Next, each embodiment of the present invention will be described based on FIGS. 1 to 6.

First, to explain the example in Figure 1, wastewater 1 is returned to sludge 2.
, the first denitrification step 4 under anaerobic conditions together with the circulating nitrification solution 3
After the NOx in the circulating nitrification liquid 3 was denitrified by the BOD component of the wastewater 10, it flowed into the first nitrification step 5 under aerobic conditions, where N1-13 of the wastewater 1 was nitrified to NOx. Afterwards, a part of it is recycled to the first denitrification step 4,
The remainder flows into the second denitrification process 6, where NOx is mainly denitrified by endogenous respiration, but in the second denitrification process 6, the water temperature is 30
About o, iq・NH3-N/r-MLSS#hr N at °C
1-13-N elutes. Denitrification rate due to endogenous respiration is 0
．． 5-1. Ot7+/r-MLSS-br Tealka et al., e.g.
0 to 20 my/l of NH3-N will be eluted in the second denitrification step 6. The eluted NH3-N is nitrified and converted to NO in the next second nitrification step 7, and then the mixed liquid flows into the first solid-liquid separation step 8, where the sludge is concentrated and separated. The sludge 2 is returned to the nitrification process 4.

Each process from the first denitrification process 4 to the first solid-liquid separation process 8 described above constitutes a high MLSS process A in which highly concentrated MLSS (activated sludge) is retained and high-load processing is performed. , MLSS is 1oooo my/1 or more, preferably 1
The concentration is maintained at a high concentration of 0,000 to 30,000 yvyt.

A sedimentation tank may be used in the first solid-liquid separation step 8, but if a mechanical solid-liquid separation method such as centrifugation or pressure flotation is used, the sludge will be retained at a higher concentration than the sedimentation method. It is possible to do so. In order to maintain a high concentration of MLSS within the process, the concentration and/or flow rate of the returned sludge 2 may be increased.

Separated water 12 from the first solid-liquid separation step 8 flows into a third deairing step 9, where NO produced by nitrification in the second nitrification step 7 is denitrified. In this third denitrification step 9, a reducing agent 14 such as alcohol may be used, or denitrification may be performed by endogenous respiration. The denitrification mixture flows into the aeration step 10 again and the residual B
After the OD is removed, the sludge is subjected to solid-liquid separation in a second solid-liquid separation step 11, and the separated water 12' is discharged or subjected to further advanced treatment. Excess sludge 13 concentrated and separated in the second solid-liquid separation step 11 is sent to a sludge treatment/disposal step.

Each process from the third denitrification process 9 to the second solid-liquid separation process 11 above constitutes a low MLSS process B.
MLSS is less than 50% of high MLSS process A ~ 1000
It is kept below 1μ.

Denitrification in the third denitrification step 9 may be performed by endogenous respiration, but if alcohol or other substances are added as the reducing agent 14, the nitrogen concentration in the separated water 12' can be further reduced. Further, in the re-aeration step 10, the nitrogen content in the sludge is eluted by self-oxidation and becomes NO.

is generated, the re-aeration liquid 1 is circulated to the third denitrification step 9 to denitrify NO due to self-oxidation.
It may be set to 5.

The concentration of excess sludge 13 in step 11 is high in the second solid-liquid portion 1.
If it is lower than the sludge 2 returned to the LSS process, the excess sludge 13 is transferred to the first solid-liquid separation process 8 as shown by the broken line, and is made into a high concentration before being pulled out (excess sludge 13'), which is convenient for sludge treatment. Good. In this case, the Yugetsu of the surplus sludge 13 flows into the third denitrification process 9, but there is no problem. Surplus sludge 1
3 is not transferred to the first solid-liquid separation process 8, there is no returned sludge, so by using an organic and/or inorganic flocculant in the water flowing into the second solid-liquid separation process 11, the separated water 12'
It is possible to completely remove COD, chromaticity components, or phosphorus in the sludge, and at the same time coagulate the sludge, so it is extremely convenient for solid-liquid separation, and the amount of coagulant added during dewatering of excess sludge 13 can be drastically reduced. . Furthermore, by adding a flocculant, it becomes possible to use a dehydrator for solid-liquid separation in the second solid-liquid separation step 11, so that the dehydrated cake with a low water content can be used as the excess sludge 13 in the second solid-liquid separation step 11. can be discharged directly from

The MLSS concentration in the low MLSS process B is determined by the amount of surplus sludge generated in the high MLSS process A. For example, if the amount of surplus sludge generated is 2 Ky/(n?・wastewater), the MLSS concentration in the low MLSS process B is determined by the amount of surplus sludge generated in the high MLSS process A.
The MLSS concentration in LSS process B is 2ooo1n/A. The MLSS of the low MI, SS step B is replenished by the MLSS of the separated water 12 of the first solid-liquid separation step 8. As the MLSSi degree increases in the high MLSS process, the sludge load in the first solid-liquid separation process 8 increases, so the separated water 1
MLSS in 2 increases, and conversely, high MLSSSS process M
When the LSS concentration decreases, the sludge load in the first solid-liquid separation step 8 decreases, so solid-liquid separation becomes sufficient, and the separated water 1
Ml and SS in 2 decreased, resulting in high MLSS culm A.
1. The ML and SS concentrations in the low MLSS step I3 converge to a constant value and reach equilibrium.

The MLSS concentration in the high MLSS step A is naturally determined by the concentration separation performance of the first solid-liquid separation step 8, but in the low MLSS
As mentioned above, MLS in step 3 is determined from the amount of sludge generated per unit volume of wastewater, and is unrelated to the performance of the first solid-liquid separation step 8.

In addition, in order to transfer the MLSS of the high MLSS process A without going through the first solid-liquid separation process 8, the effluent from the second nitrification process 7 may be directly supplied to the third denitrification process 9.

In other words, the sludge replenishment pipe 16 can be used 1 (therefore, the MLSS concentration in the low MLSS process B can be temporarily increased, so the sludge load in the first solid-liquid separation process 8 can be temporarily reduced due to the decrease in the flow rate of the wastewater 1). When the MLSS concentration in the low MLSS process B decreases and solid-liquid separation is complete, the MLSS concentration in the low MLSS process B can be controlled by replenishing sludge.

Next, a second embodiment of the present invention will be explained with reference to FIG. This is suitable for the treatment of wastewater 1 which has a high nitrogen concentration and relatively few sludge-forming groups, and is suitable for treating wastewater 1 that has a high nitrogen concentration and relatively few sludge-forming groups.
OneThrough's method is employed when the MLSS concentration in the low N1LSS process cannot be maintained sufficiently.

Regarding the configuration and functions of this embodiment, its high MLSS
The process is the same as the example in Figure 1, and the low M LSS process is the first
It is almost the same as the example shown. The low MLSS process will be explained below.

The separated water 12 flows into the third denitrification process 9 together with the returned sludge 2', where it is denitrified with or without the addition of a reducing agent 14, and then passes through the re-aeration process 10 to the second solid-liquid separation process 11.
A part of the separated sludge becomes return sludge 2' to the third denitrification process 9. Note that, in the second solid-liquid separation step 11, a flocculant is added as in the example in FIG. 1, and a dehydrator cannot be applied to the second solid-liquid separation step 11.

Next, the third aspect of the present invention. 4th. The fifth and sixth embodiments will be explained based on FIGS. 3, 4, 5, and 6, respectively.

In both the example shown in FIG. 3 and the example shown in FIG. The nitrification of NH3 is mainly carried out at the ridge stage of the first solid-liquid separation step 8.

The embodiments shown in FIGS. 5 and 6 are adopted when there is no BOD component available for denitrification in the wastewater 1. When treating such wastewater 1, denitrification may be carried out by adding alcohol or other reducing agent to the first denitrification step 4 of the flow shown in FIGS. 1 to 4. The flow shown in the figure is simpler in terms of process. Note that the circulating denitrification liquid 17 is circulated to the first nitrification step 5 to neutralize the pH of the first nitrification step 5, which decreases due to nitrification of NH3, with its alkaline content, thereby preventing a decrease in activity due to a decrease in the pH of nitrifying bacteria. That is. Therefore, wastewater with low NH3 concentration, p
The circulation of a denitrifying solution is not necessary for the treatment of wastewater that has a high H buffering capacity and whose pH does not decrease due to nitrification.

In addition, in FIGS. 3, 4, and 6, 10b is the second
This is the re-aeration process.

The re-aeration process tank installed in the examples in Figures 1 to 6 above is a small tank with a residence time of about 1 to 3 hours for the inflow water, and the fine N2 gas in the denitrification liquid is The main purpose is to aerate and dissipate dissolved N2 gas to facilitate solid-liquid separation, and to remove the OD component that remains in the denitrification solution, but the method and requirements for solid-liquid separation are Depending on the quality of the water, this may not be necessary, and it is advisable to consider in advance whether the re-aerating process is necessary or not when applying the present invention.

Further, the present invention can be fully applied to processes using other denitrification methods, such as aerobic denitrification methods.

Next, embodiments of the present invention will be described.

This was done for both the flows shown in Figures 1 and 2. Also, the second
In the embodiment according to the figure, the activated sludge for replenishment via the sludge replenishment pipe 16 is used as the SS overflowing from the settling tank adopted as the first solid-liquid separation step 8, and the third
It was not transferred to denitrification step 9. The wastewater used was sludge-removed human urine and artificial wastewater.

The treatment conditions are shown in Table 1, and the treated water quality is shown in Table 2. .

Table 2 shows the treated water quality when ethanol was not added 17 in the third denitrification step 9.

Table 1 Treatment conditions Table 2 Treated water quality (unit: liters) [Note] (1) *IT-N:NHa-N+N0x-N
(2) *-2 1° corresponding to separated water 12 (3) *-
s corresponds to separated water 12'.

(4) Second denitrified water has the quality of treated water using conventional high MLSS internal 1yk type denitrification. Next, an example in which the removed human urine was treated at low water temperature according to the flow shown in Figure 1. I would like to add a note about this.

The treatment conditions at this time were a throughput of 50 t/day, a water temperature of 0.degree. C., and the other conditions were the same as those for the sludge-removed human waste shown in Table 1.

Note that although the NH3-N of the slag-removed human urine used was almost the same as that in Table 2, the SS concentration was higher than that in Table 2.

The quality of the treated water is almost the same as in Table 2, NH
3-N2η4. It was NO ANY 31 DA 4. Also ML
The SS concentration was 31000 qS in the first nitrification tank and the second denitrification tank, and 9900 mVt in the second nitrification tank.

An experiment was attempted in which the MLSS concentration in the first nitrification tank was raised to about 35,000 myA, but the high MLSS concentration increased the viscosity and made it difficult for the aerated air to escape from the nitrification tank. entrained and inhibited denitrification. From this, the M of the nitrification and denitrification process that uses highly concentrated activated sludge
It is determined from the examples that the LSS concentration is preferably 10,000 to 32,000 4. In addition, in the low water temperature example, when the MLSS concentration in the second nitrification tank is 9900 cm, T-N is 5 and 4. The value is almost the same as the treated water quality in Table 2, but it is somewhat worse. From this, the MLSS concentration in the nitrification and denitrification process using low-concentration activated sludge is preferably 10,000 to 4 or less, more preferably within the range shown in Table 2, that is, 1,500 to 7,500#vA tonal.

As described above, the present invention has a high concentration of ML in the treatment process.
By maintaining SS, it is possible to reduce the size of the denitrification tank through endogenous respiration, significantly reduce the cost of additives such as methanol and ethanol, or eliminate them. Signs of LSS concentration by endogenous respiration denitrification method. It is possible to achieve great effects, such as being able to remove nitrogen at an extremely high rate.

[Brief explanation of the drawing]

1 to 6 are flow sheets showing each embodiment of the present invention. A...High MLSS process, B...Low MLSS
Process, 1...wastewater, 2,2'...return sludge, 3...
・Circulating nitrification liquid, 4... First denitrification process, 5... First nitrification process, 6... Second shedding process, 7... Second nitrification process, 8... First solidification Liquid separation step, 9...Third denitrification step,
10... Re-aeration step, 10a... First re-aeration step, 10b... Second re-aeration step, 11... Second solid-liquid separation step, 12, 12'... Separation water, 13, 1
3'... Surplus sludge, 14... Reducing agent, 15... Circulating re-aeration liquid, 16... Sludge supply piping, 17... Circulating denitrification liquid. Patent applicant Minoru Sen 1) Patent attorney representing Ebara Infilco Co., Ltd.

Claims (1)

[Claims] 1. A method for biological nitrification-denitrification bed treatment of wastewater,
The first stage is a high MLSS process consisting of a nitrification-denitrification process and solid-liquid separation process (1) that uses high-concentration activated sludge, and the second stage is a nitrification-denitrification process and solid-liquid separation process (1) that uses low-concentration activated sludge. A low MLSS process consisting of It) is installed, and the wastewater is subjected to nitrification and denitrification treatment at a high load in the high MLSS process,
The separated water from the solid-liquid separation step (1) is converted into the low MLSS
A biological nitrification and denitrification method for wastewater that is characterized by not undergoing nitrification and denitrification treatment during the process. 2. The high MLSS step includes a first denitrification step, a first nitrification step, a second denitrification step, a second nitrification step, and the solid-liquid separation step (
It is constructed by combining 1) in this order,
1. The low MLSS step is configured by combining the third denitrification step, the re-aeration step, and the solid-liquid separation step (II) in this order. The method according to claim 1, which is a method according to claim 1. 3. The third denitrification step is the solid-liquid separation step (if)
3. The method according to claim 2, wherein the method is carried out by returning the thickened sludge produced by the method. 4. The high MLSS process is a first denitrification process, a first nitrification process, a second denitrification process, and a first re-aeration process. The solid-liquid separation step (1) is combined in this order, and the low MLSS step includes a second nitrification step, a third denitrification step, a second re-aeration step, and the solid-liquid separation step. The method according to claim 1, which is constructed by combining (n) in this order. 5. The method according to claim 4, wherein the second nitrification step is performed by returning the concentrated sludge from the solid-liquid separation step ([). 6. The high MLSS step is the first nitrification step, the first
The denitrification step, the second nitrification step, and the solid-liquid separation step (1) are combined in this order, and the low ML S S step is the second denitrification step. Claim 1, which is configured by combining the re-aeration step and the solid-liquid separation step (■) in this order.
The method described in section. 7. The high MLSS step is configured by combining the first nitrification step, the first denitrification step, the first re-aeration step, and the solid-liquid separation step (1) in this order, and the low MLSS step Claim 1, wherein the steps are a second nitrification step, a second denitrification step, a second re-aeration step, and the solid-liquid separation step (['l] are combined in this order). Method. 8. The nitrification and denitrification step of the high MLS S step is
At LSS10000-32000 mf/l, the low M
The nitrification and denitrification process of the LSS process is performed using MLSS1500-75.
Claims 2 and 4, respectively, filed under 0094
Section. The method described in paragraph 6 or 7.