JPS58139792A - Treatment of organic waste liquid - Google Patents

Abstract

PURPOSE:To remove phosphorus simultaneously with BOD and nitrogen efficiently from org. waste liquid, by treating liquid to be treated anaerobically by the use of settled sludge which is subjected to denitrification and concn. and oxidizing the same biologically then separating the liquid to treated liquid and settled sludge. CONSTITUTION:In an activated sludge method by an anaerobic-aerobic method, liquid 11 to be treated which is org. waste liquid and concd. sludge 17 are introduced into an anaerobic tank 1, where both are agitated and mixed in the substantial absence of dissolved oxygen and NO<->x to remove at least part of BOD. The mixed liquid anaerobically treated in such a way is introduced into an aerobic tank 2, where gases 20 contg. oxygen, separated liquid 16 contg. NO<->x, settled sludge 15, etc. are added to the liquid to remove BOD, phosphorus, etc. and to convert NH<->4 to NO<->x. The mixed liquid 13 biologically oxidized by such treatment is introduced into a final settling basin 3, where the liquid is separated to treated liquid 14 and settled sludge 15. The settled sludge 15 is so controlled as to contain >=1mg/l NO<->x-N and the controlled sludge is introduced into a denitrifying-concentrating tank 4, where separated liquid 16 is separated, and concd. sludge 17 contg. NO<->x-N controlled to <=0.5mg/l is obtained. The concd. sludge is used for the anaerobic treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating domestic wastewater or similar organic wastewater, and particularly relates to an anaerobic method for removing phosphorus from organic wastewater at the same time as BOD, or at the same time as BOD and nitrogen. - This relates to the improvement of a biological treatment method called aerobic method.

In general, the anaerobic-aerobic method is a biological treatment method developed in the Federation of South Africa around 1975-1976, in which DO(
An anaerobic tank is installed in which neither dissolved oxygen nor NO exists, and the liquid to be treated is mixed and stirred with the returned dirt and mud before the subsequent DO.
Alternatively, it was a technology that led to a biological oxidation tank where NOx was present. In this way, by modifying the process structure of the activated sludge method or the circulating nitrification-denitrification method, activated sludge with a high phosphorus-containing capacity can be selectively produced, and BOD can be reduced from organic wastewater.
Proponents of this technology claim that it can remove not only nitrogen but also phosphorus with high efficiency. (For example, J,
L, Barnard: A Revue of B
iological PhosphorusRemov
Al in the Activated Sludge
e Process Water S AVol, 2
NJII 3 July 1976) The inventors also became interested in this technology and continued research using pilot plants, etc., using synthetic sewage and domestic wastewater discharged from housing complexes as liquids to be treated.As a result, many improvements were made to this technology. It was recognized that there were things that needed to be done.

Among these confirmed characteristics, the following two points are related to the present invention.

1) In order to achieve good phosphorus removal with this technology, the anaerobic tank must not only be free of DO and NO in a dynamic equilibrium state, but also have a minimum amount of NOx inflow. What you need to do.

If) If the settled activated sludge is left in the final settling tank for a long time, the bottom of the pond will not be in an anaerobic state without the presence of Do or NO; PO4 will be released from the settled activated sludge, which will increase the P04P@ level of the treated liquid. . Therefore, to prevent this,
It is necessary to remove settled activated sludge from the final settling tank relatively quickly.

These two points are not particularly novel findings, but are well-known operational management matters. However, it is quite far, if not impossible, to simultaneously achieve these two matters in the technical form of conventional anaerobic-aerobic methods. In particular, it is difficult to suppress the amount of NO flowing into the anaerobic tank in item 1) because NOx is generated within the system and often flows together with the returned sludge. In the conventional anaerobic-aerobic method, as a preventive measure, it is recommended to store the settled activated sludge for a long time in the final settling tank to promote DO consumption and subsequent denitrification (N6) there.

However, in this conventional anaerobic-aerobic activated sludge method, the final sedimentation tank has three functions: solid-liquid separation, concentration of settled sludge, and denitrification, so settling sludge is deposited at the bottom of the final settling tank. The operation of storing the sludge for a long time often resulted in excessive anaerobic conditions, resulting in an adverse phenomenon in which PO4 eluted from the settled sludge was mixed into the treated solution. That is, this operation not only has the risk of increasing the POa concentration in the treatment liquid as described in item II), but also has the drawback of contaminating the treatment liquid with scum and the like accompanying denitrification.

The present invention aims to eliminate these problems appropriately, and eliminates the trade-offs of the final sedimentation tank operation that the conventional anaerobic-aerobic method has, and removes BOD and phosphorus at the same time. The purpose of this method is to provide an anaerobic-aerobic method that suppresses the amount of NOx in the returned sludge flowing into the anaerobic tank and does not increase the scum turbidity or PO4 concentration in the treated liquid and is easy to manage. .

Another object of the present invention is to provide an anaerobic-aerobic method that can reliably supply thick returned sludge to the anaerobic tank without promoting denitrification in the final settling tank, thereby greatly improving treatment efficiency. be.

The feature of the present invention is that the settled sludge separated by precipitation in the final settling tank is guided from the final settling tank to the denitrification/concentration tank where it is concentrated while promoting denitrification, and at least a part of the resulting concentrated sludge is The sludge is supplied to the anaerobic tank as returned sludge, and the separated liquid from the thickening tank is led to one of the processing tanks following the anaerobic tank for treatment.

With this process configuration, there is no need to promote denitrification in the final sedimentation tank, so there is no need to increase the concentration of Pony or turbidity in the treated solution, and the returned sludge sent to the anaerobic tank is thick. No. Inflow into the cypress can be kept to a minimum, if any, and highly efficient and stable processing is possible.

To explain a typical example of the anaerobic-aerobic method shown in the drawing in the embodiment of the present invention ψ, Fig. 1 is an example of an embodiment applied to the activated sludge type anaerobic-aerobic method. The liquid 11 is led to the anaerobic tank IK, which becomes the first tunnel, and Do
The sludge is mixed with the concentrated sludge 17 sent from the denitrification/concentration tank 4 and subjected to anaerobic treatment in the absence of NOx or NOx.

During this anaerobic treatment process, the activated sludge hydrolyzes the polyphosphoric acid accumulated within its cells into PO4 and releases it into the solution. In parallel, the activated sludge contains BOD present on the solution side, that is, the treated liquid contains 9 BO
At least a portion of D is ingested in a non-oxidative manner and stored within cells as intracellular organic matter. The anaerobically treated mixed liquid 12 thus generated is led to an aerobic tank 2 where it is aerated with an oxygen-containing gas 20 such as air or oxygen-enriched air, where it undergoes aeration treatment and undergoes the second step. Complete. In this aeration process, that is, the second step, activated sludge oxidizes the intracellular organic matter and the BOD on the solution side that could not be taken in during the anaerobic treatment process, and the PO4 present on the solution side is coupled with the oxidation reaction.
is taken into cells and accumulated as polyphosphate. If conditions such as liquid temperature, sludge age, and pH allow nitrifying bacteria to coexist in activated sludge, the nitrifying bacteria that coexist in activated sludge during the aeration process will be transferred to the solution side through the following successive reactions. It oxidizes the nitrogen present in NO2 to NOs.

2N) i: +302→2NO2+ 2H20+ 4H
j2NO: + 02 → 2NOg In this way, the BOD and PO4 on the solution side are sufficiently reduced, and depending on the processing conditions, the aerated mixed liquid 1 may also contain NOx.
3 is supplied to the final settling tank 3 of the third step, where it undergoes solid-liquid separation and is separated into a treated liquid 14 and settled sludge 15. This final settling tank 3 is operated with solid-liquid separation as its main function, and is operated in such a manner that NOx remains in the settled sludge 15 at all times, with the principle that an excessive amount of settled sludge is not stored at the bottom of the tank.

In this operation method, the precipitated sludge 15 is denitrified and concentrated in the concentration tank 4.
A NOx concentration detector 22 such as a NOs ion meter or an oxidation-reduction potentiometer may be installed in the path for transferring the sludge to the sludge, and the flow rate of the settled sludge transfer pump 21 may be controlled using this electrical signal. In this case, No. remaining in the settled sludge 15;
The concentration is preferably lq/j or more.

Further, the settled sludge 15 that has been separated by precipitation in the final settling tank 3 is led to the denitrification/concentration tank 4 which is the fourth step via the settled sludge transfer pump 21, where it is reconcentrated to form the separated liquid 16 and the concentrated sludge. It is divided into sludge and 17. As for the structure of this lifesaving concentration tank 4, the technology used in conventional concentration tanks can be used as is, but it is operated with a different intention from that of the final sedimentation tank 3. In other words, - Even if PO4 is eluted from the thickened sludge and mixed into the separated liquid, or even if denitrification scum is generated and the separated liquid is polluted, the thickened sludge 17 is kept at the bottom of the tank for a long time (for domestic wastewater treatment). In principle, the sludge is retained for 2 to 12 hours to promote denitrification, and preferably the thickened sludge 17 drawn from the bottom of the tank is substantially free of NOx (the NOx N concentration is 051 or less). - This can often be achieved by simple sludge residence time control;
For example, NO is added to the route that returns the thickened sludge 17 to the anaerobic tank 1.
This can also be achieved by providing a NOx s* detector 22 such as an x-ion meter or an oxidation-reduction electrometer, and controlling the flow rate of the thickened sludge return pump 23 using this electric signal.

Further, the separated liquid 16 discharged from the upper part of the concentration-denitrification tank 4 often contains denitrification scum and has a higher PO4 concentration than the treated liquid 14. Furthermore, if the amount of settled sludge 15 to be transferred is excessive, carryover of the activated sludge itself may be avoided. Therefore, this was considered to be equivalent to treatment liquid 14 and was discharged. Since it is not preferable to send the separated liquid 16 to an advanced treatment process, a treatment tank for the liquid 11 to be treated prior to the anaerobic process 111, such as a primary settling tank (not shown), is also considered as a discharge destination for the separated liquid 16. However, even if the thickened sludge 17 is completely denitrified, the separated liquid 16
In many cases, NOx remains in the anaerobic tank, and if this is first led to the settling tank and mixed with the liquid to be treated 11, there is a risk that NOx will often flow into the anaerobic tank 1. Therefore, in the present invention, the first As shown in the example, the separated liquid 16 is introduced into the aerobic tank 2. Because the treatment process of aerobic tank 2 is No;
is not affected by the presence or absence of P contained in the separated liquid 16.
This is because O4 can be retaken into activated sludge cells, denitrification scum can also be destroyed, and it can be converted into normal activated sludge flocs.

When this separated liquid 16 is introduced into the aerobic tank 2, the activated sludge concentration (MLSS concentration) in the aerobic tank 2 becomes lower than that in the anaerobic tank 1, and the capacity of the aerobic tank 2 is free. If so, there is no problem with the processing. However, in order to reduce the capacity of the aerobic tank 2, the higher the activated sludge concentration in the aerobic tank 2, the better. One way to increase the activated sludge concentration in the aerobic tank 2 is to divert a part of the thickened sludge 17 and guide it to the aerobic tank 2.
Since the inflow of NOx can be pumped into the tank, diverting the thickened sludge 17 with sufficiently reduced NO; to the aerobic tank 2 is somewhat difficult from the viewpoint of effectively utilizing the facility capacity of the denitrification/thickening tank 4. Since there is a problem, as shown in the example in FIG. 1, a part of the activated sludge settled in the final settling tank 3 is returned to the aerobic tank 2 by the pump 21' as a short-circuit return sludge 18 to reduce the capacity of the denitrification/concentration tank 4. It is better to save money.

Incidentally, the surplus sludge 19 generated by the natural process may be pulled out from the denitrification/concentration tank 4 as shown in the example in FIG.
You may pull it out further. Furthermore, if strict sludge age control is to be performed, it is conceivable to use a portion of the aerated mixed liquid 13 as surplus sludge.

FIG. 2 shows an example of an embodiment when applied to a circulating nitrification-denitrification type anaerobic-aerobic method, in which the liquid to be treated 11 is led to the anaerobic tank 1, and the re-denitrified liquid is sent from the re-denitrification tank 6. It is mixed with sludge and subjected to anaerobic treatment in the first step. (The operation of this anaerobic treatment is the same as the example in Figure 1.) The anaerobically treated mixed liquid 12 is sent to the denitrification tank 7, where it is sent to the subsequent nitrification tank 8.
The circulating liquid 26 sent from the final settling tank 3, the short-circuit return sludge 18 sent from the final settling tank 3, and the separated liquid 16 sent from the denitrification/concentration tank 4 are mixed, and the N contained in each of these liquids is mixed.
O; is denitrified. In this denitrification process, activated sludge oxidizes the intracellular organic matter and BOD present in the solution, and conjugates with the oxidation reaction to take POa- present in the solution into the cells, converting it into polyphosphoric acid. Accumulate in.

The denitrification mixed solution, that is, the anaerobically treated mixed solution 12 thus generated is led to the nitrification tank 8 where it is exposed to oxygen-containing gas in a second step, and undergoes nitrification treatment. In this nitrification process, - present on the solution side is nitrified and converted into NOx. Also, in this process, the activated sludge further oxidizes intracellular organic matter and solution side BOD, and at the same time further takes in PO4 from the solution side. A part of the nitrified mixed liquid containing NOx generated in this way is sent to the denitrification tank 7 as the circulating liquid 26, while the remaining nitrified mixed liquid part is
The sludge is led to the final settling tank 3 that controls the process, where it is separated into a treated liquid 14 and settled sludge. A part of the settled sludge 15' is transferred to the denitrification concentration tank 4 via the settled sludge transfer pump 21 to complete the fourth step. This settled sludge transfer pump 2
The flow rate of No. 1 can be controlled in the same manner as the example in FIG. The remainder of the settled sludge is sent to the denitrification tank 7 or the nitrification tank 8 as short-circuit return sludge 18.
It is sent selectively or separately.

The settled sludge 1 is sent to the denitrification concentration tank 4 by the pump 21'.
5' is divided into a separated liquid 16 and a thickened sludge 17. The denitrification/concentration tank 4 in the example shown in FIG. 2 is also operated in the same manner as in the example shown in FIG. However, if the system as a whole is operated with an excessively low F2-M ratio [ratio between the daily BODil (F) brought in by the liquid to be treated and the MI of the aerobic tank (M)], the settled sludge will be introduced into the system. Since the activated sludge 15' is stabilized, the denitrification rate is low even if it is concentrated, and sometimes the NOx concentration in the concentrated sludge 17 cannot be reduced sufficiently.

As a countermeasure against such a case, in the example shown in FIG. 2, the concentrated sludge 17 is led to the re-denitrification tank 6, and there is a cloth 4 for denitrification such as methanol! ! ! Denitrification is completed by adding chemicals 4, etc., and the re-denitrified sludge 28 discharged from there is treated as anaerobic 1! ! 1
is being sent to. In the example shown in FIG. 2, the excess sludge 19 is drawn out from the denitrification/condensation tank 4 so that the treatment operation can be carried out stably.

In the present invention, the settled sludge separated by precipitation in the final settling tank is guided from the final settling tank to the denitrification/concentration tank where denitrification is promoted while being concentrated, and at least a part of the obtained thickened sludge is returned to the sludge. BOD and phosphorus can be simultaneously removed accurately and efficiently from the organic waste liquid by supplying the separated liquid from the concentrating tank to one of the treatment tanks following the anaerobic tank. NO of return sludge flowing into tank
- Operation management that can control the amount and do not increase the concentration of scum turbidity or PO4 in the treated liquid is easily possible, and the clarity of the treated liquid is greatly improved, without accelerating denitrification in the final settling tank. It is possible to reliably supply thick return sludge to the anaerobic tank, greatly improving treatment efficiency.

Next, examples of the present invention are listed together with comparative examples of conventional methods. It has been demonstrated that the method of the present invention provides good results.

[First Comparative Example] The inventors used a conventional activated sludge type anaerobic method using domestic wastewater mixed with domestic sewage and human waste as the liquid to be treated.
The aerobic activated sludge method was further tested using a pilot plant. The specifications of this pilot plant are shown in Table 1.

Table 1 The conventional pilot plant specification test started in early spring, with a flow rate of the liquid to be treated of 5.45 rrl for 1 day.
The process was started under a flow rate condition of a return rate of 30- (return sludge flow rate: 1.63 rp/7 days), and at the beginning of 6, no nitrification occurred at all, so relatively good treatment results were obtained. However, as the air temperature and the temperature of the liquid to be treated rose, nitrification gradually progressed in the aerobic tank, and by the end of April, the nitrification rate had reached 8,096. Around this time, the oxidation-reduction potential of the oxidation-reduction potential needle consisting of a platinum-silver chloride electrode installed in the anaerobic tank was lowered to 420 m.
The amount of PO4 released in the anaerobic tank decreases, and the POJ f of the treated liquid increases from less than
Ik degree has also increased. At this time, when the oxidation-reduction potential of the returned sludge was measured, it was -220 to -200 mV, and 2 to 4 IIf/l of Now-Nf1M was detected on the solution side. In addition, the volume of settled sludge in the final settling tank is 0.110-
So, the residence time of settled sludge calculated from this (settled sludge volume/return sludge flow rate) is 16 hours, and return sludge concentration FiM
It was expressed in LSB and was 1200011II/l.

[Second Comparative Example] Since the phosphorus removal performance of the second comparative example deteriorated, on May 10th, in order to solve this problem, the return sludge rate was changed to 15 cm (return sludge flow rate 0.82 d7 days). Moreover, the volume of settled sludge in the final settling tank was controlled at 0.18 OFF/.

As a result, the residence time of the settled sludge in the final settling tank was extended to 5.3 hours. As a result, the MLSS concentration in the returned sludge was 20,500 m/l, and the NO;N concentration on the solution side of the returned sludge was below the detection limit. In addition, the oxidation-reduction potential began to decrease at both the return sludge and the anaerobic tank outlet, and both became -450 mV or less. In parallel with such a decrease in redox potential, the PO4 release (in the anaerobic tank) and PO4 uptake (in the aerobic tank), which are unique to anaerobic-aerobic activated sludge, have become remarkable. However, the processing liquid POA
The Pa degree was higher than that at the start of the test, and the clarity of the treated solution was also deteriorated due to the removal of scum. Solubility Po4 of the liquid to be treated, the anaerobically treated mixed liquid, the aerobically treated mixed liquid and the treated liquid
The average values of P concentration were 3.3, 17.2, and 00, respectively.
4,052 (animal t), and although the concentration was sufficiently low in the aerobically treated mixed solution, it was high in the treated solution.

We thought that the cause of this was probably that PO< eluted from the activated sludge stored in the final settling tank was mixed into the treated solution, and when we measured the solubility of the returned sludge, PO4-PI3 degrees, we found that it was actually more than 30 ■/LhsP. was also eluted. From this experience, it has been found that completing denitrification in the final sedimentation tank risks increasing the PO4 concentration of the treated solution.

Example-1 Based on this experience, the first comparative example was tested in parallel with the second comparative example test.
A pilot plant test of the method of the present invention was conducted in accordance with the illustrated example. The specifications of this plant are shown in Table 2. The denitrification tank is a circular clarifier of the same type as the final sedimentation tank, but the rake is equipped with pickets to facilitate concentration.

The flow rate of the liquid to be treated is as follows. 5.5, which is almost the same as the second comparative example.
2 m'/day, and other flow conditions are: short-circuit return sludge (final settling tank → aerobic tank): 0.62 m'/day; return settled sludge (final settling tank → denitrification thickening tank): 1.22 m'/day
Separation liquid (denitrification concentration tank → aerobic cypress): 0.
90W? /day return thickened sludge (denitrification thickening tank → anaerobic cypress)
: 032 m'/day. Also, the volume of settled sludge in the final settling tank is 0.085? (Settled sludge retention time 0.0
85 x 24 / (0,62+ 1.22) = 1
．． 1 hour), and the volume of concentrated sludge in the denitrification-thickening tank is 0.1
20m' (thickened sludge retention time 0.120 x 2410
．． 32 = 9.0 hours).

As a result of such operating operations, the concentration of the short circuit return sludge and transferred precipitated sludge drawn from the final ratio pond decreased to 95,001 Ni/l as MLSS, but that of the concentrated return sludge reached 36,000 η/l. In addition, the redox potential of the settled sludge drawn out from the final settling tank by the platinum-silver chloride electrode is -50 to -170 mV, and 6 to 8 W/A (average 7
．． 511f//-) NOx N was detected. Final - There is no release of PO4 from activated sludge in the settling tank,
Soluble PO4-P in the settled sludge had almost no difference from that in the aerobically treated mixed liquor, and was always below 0.1 wsp/L. On the other hand, the oxidation-reduction potential of concentrated return sludge is -
From 480 to -490 mV, no NOz N was detected. Due to such high anaerobic degree, a large amount of phosphorus was released in the de-nitrogen concentration tank, and the soluble PO4-P in the concentrated return sludge reached 95 q/l.

Correspondingly, the separated liquid overflowing from the denitrification-concentration tank to the aerobic tank contained 3.2 W/l of soluble PO4-P, which had no effect on the overall system treatment. had no adverse effects.

Typical water quality data of Example-1 is shown in Table 3 in comparison with that of the second comparative example. The difference in water quality between the two treated solutions is largely reflected in the concentration of soluble POa-P. Comparative example-2
In this case, since PO4 is released from activated sludge in the final settling tank, the PO4-P concentration of the treated liquid is
Table 3: Processing results of Example 1 and Comparative Example 2 is higher than that of Example 1. Also in terms of the clarity of the treatment liquid, Example-1
Since the amount of denitrification in the final settling tank is small, there is also less denitrifying scum. Therefore, the SS concentration in the processing solution is low, and correspondingly the solid BOD (the difference between total BOD and soluble BOD)
The concentration of solid P (difference between total-P and PO4-P) is also lower. On the other hand, in the second comparative example in which denitrification is promoted in the final settling tank, the presence of denitrifying scum improves the clarity of the treated liquid, and the SS concentration and solid BOD
The temperature was 111 degrees, and the concentration of solid P was high, and the difference between the two was clear.

Example 2 A treatment test was conducted in an indoor-scale experimental facility using organic wastewater discharged from a food processing factory as the liquid to be treated according to the method shown in Figure 2, excluding the re-denitrification tank. Table 4 shows the specifications of this experimental facility.

Table 4 Experimental Facility of Example-2 The liquid to be treated was stored in a refrigerator and pumped from there into an anaerobic tank under the following flow conditions.

Liquid to be treated: 144t/daily circulating liquid (
Nitrification tank→Denitrification tank); 415t/day Short-circuit return sludge (Final settling tank→Denitrification paddle): 63t/day Transfer settled sludge (
Final sedimentation tank → denitrification concentration tank): SOZ/day separation
Liquid (denitrification concentration tank → denitrification cypress); 571/day return thickened sludge (denitrification concentration tank → denitrification cypress); 23t/day
The volume of settled sludge in the settling tank at the end of the day was controlled at approximately 14 tons, and the volume of concentrated sludge in the denitrification thickening tank was controlled at approximately Ut. As a result, the respective sludge retention times were 2.3 hours and 25 hours. The data average values of activated sludge concentration (MLSS), NoxN concentration, dissolved, and POaP concentration for each solution are shown in Table 5.
Table 6 shows the average treatment results for the entire system.

Table 6 Based on the treatment results of Example-2 and the second comparative example, the PO4-
It became clear that the P# degree and clarity were greatly improved.

[Brief explanation of drawings]

The drawings show an embodiment of the method of the present invention, and FIG. 1 is a system explanatory diagram, and FIG. 2 is a system explanatory diagram of another embodiment. 1...Anaerobic tank, 2...Aerobic tank, 3...Final sedimentation tank, 4...Denitrification-concentration tank, 6...Re-desorption tank, 7...
Denitrification tank, 8... Nitrification tank, 11... Liquid to be treated, 12.
...Anaerobically treated mixed liquid, 13...Aerated mixed liquid,
14...Treatment liquid, 15°15'...Settled sludge, 16.
...Separated liquid, 17...Thickened sludge, 18...Short circuit return sludge, 19...Excess sludge, 20...Oxygen-containing gas,
21...Settled sludge transfer pump, 21'...Pump,
22... Now concentration detector, O... Thickened sludge return pump, 25... Nitrification mixed liquid, 26... Circulating fluid, Seki-
... Re-denitrified sludge, 29... Organic chemicals for denitrification. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Go Hayama - Patent attorney Sen 1) Minoru

Claims (1)

[Claims] 1. The liquid to be treated and the concentrated activated sludge are brought into contact and mixed in a state in which dissolved oxygen, nitrate radicals, and nitrite radicals are substantially absent, and the anaerobically treated mixed liquid is obtained. a first step of producing a biologically oxidized mixed solution; a second step of introducing the anaerobically treated mixed solution and contacting and mixing it with at least a portion of oxygen, nitrate, or nitrite to produce a biologically oxidized mixed solution; A third factory which introduces the biologically oxidized mixed liquid and separates it into solid and liquid to produce a treated liquid and precipitated activated sludge, and at least a part of the precipitated activated sludge produced in the mosquito third step. Let me introduce it,
A method for treating organic waste liquid, which comprises a fourth step of concentrating this to produce a separated liquid and concentrated activated sludge that can be used in the first process. 2.%#'F In the method according to claim 1, a part of the settled activated sludge produced in the third step is transferred to the second step.
A method that is introduced into a process and processed. 3.4! In the method according to claim 1 or 2, the precipitated activated sludge produced in the third step is
A method in which flow 1 is controlled so that it contains NOx/N or more at the time of discharge from the process. 4. In the method according to at least one of claims 1 to 3, the concentrated activated sludge produced in the fourth step contains NOx N at the time it is introduced into the first step. A method in which the flow is controlled so that it contains 0.51111/L without exception. 5. A method according to at least one of claims 1 to 4, in which the separated liquid produced in the fourth step is introduced into the second step. i The method according to claim 5, wherein the second
A method in which the process consists of a denitrification process and a nitrification process, and the nitrification mixture that has undergone denitrification and nitrification is introduced into the final settling tank.