JPS5851991A - Treatment of odorous waste water with active sludge - Google Patents

Abstract

PURPOSE:To efficiently deodorize odorous waste water, by aerating active sludge poured into the first aerating cell with exhaust gas from the second aerating cell and the following ones, transferring the active sludge to the second aerating cell into which the odorous waste water is poured, and then aerating the sludge with air or the like. CONSTITUTION:Active sludge 16 is let flow through an inflow opening 10 into the first aerating cell 1 and aerated with exhaust gas 20 therein to deodorize odorous substance in the exhaust gas 20. The aerated active sludge 16 is then introduced through a circulating opening 23 into the second aerating cell 2. Odorous waste water 17 is let flow through an inflow opening 11 into the second aerating cell 2, agitated and mixed with the active sludge 16 by a surface aerator 5, and aerated with exhaust gas from the third aerating cell 3 to form mixed liquid 18. The mixed liquid is introduced through a circulating opening 24 into the third aerating cell 3, aerated with fresh air 19 to concurrently remove odorous components and BOD and then drained through an outflow opening 15. In this way, the concentration of oxygen dissolved in the mixed liquid inside the final aerating cell becomes at 1.5-5ppm.

Description

[Detailed Description of the Invention] This method treats organic pollutants in odor wastewater generated at kraft pulp factories, etc., and at the same time deodorizes it, and
The present invention relates to a method for simultaneously deodorizing the malodor generated during the treatment.

H2O), methyl mercaptan (MM), dimethyl sulfide (DMS), dimethyl sulfide (DMDS
) and other sulfur compounds.

A common method for treating these odorous substances is to seal the device, collect the gases, and burn them.

On the other hand, regarding methods for deodorizing odor wastewater such as vE drain and unfiltered blow condensate generated in the vacuum evaporation process of cooking black liquor,
A stripping method in which combustion is performed by expulsion with steam or air is commonly used.

However, this stripping method has the drawbacks of not only high equipment costs but also high energy consumption.

At kraft pulp mills, a large proportion of water is recycled in order to make effective use of water, so the wastewater is especially BO
It is characterized by a high D value, and many factories have activated sludge equipment as wastewater treatment equipment. It would be advantageous if this activated sludge treatment equipment could be used to simultaneously remove BOD + COD and remove odor components from odor wastewater.

In recent years, many studies have been conducted on deodorizing methods for odoriferous wastewater using activated sludge treatment. There is also a known deodorizing method for odor-smelling wastewater, which involves aeration using a gas with an oxygen content of at least 85 cm or more so that dissolved oxygen in the mixed liquid at the outlet of the aeration tank becomes 5 ppm or more. In order to prevent odorous substances contained in wastewater from dissipating into the gas phase,
This method is preferable because the amount of exhaust gas is small, but the production cost of the supplied oxygen-containing gas is high, and the pH of the treated material decreases as a result of oxidative decomposition of organic matter by the supplied gas, so it has the disadvantage that the pH must be controlled in advance. ing.

The present invention provides a method for deodorizing odor-smelling wastewater using activated sludge using air, which efficiently deodorizes the wastewater including the odor that has migrated into the exhaust gas, and also decomposes and removes the contained organic pollutants. .

That is, according to the present invention, at least two or more covered aeration tanks are provided, domestic sludge is put in the first aeration tank, and exhaust gas from the second aeration tank is finally guided to the first aeration tank. aerate,
At the same time as oxygen is supplied to the first aeration tank, odor gas substances contained in the exhaust gas are removed by activated sludge and exhausted to the atmosphere. Exhaust gas here refers to fresh air introduced into the aeration tank by an exhaust fan, blower, etc., which is aerated in the tank, and the odorous substances in the odor wastewater transferred into the air.Each aeration tank contains odor gas. refers to the gas emitted from

Next, the activated sludge liquid in the first aeration tank is transferred to the second aeration tank.
This is a method of deodorizing smelly wastewater using activated sludge, which is characterized in that the smelly wastewater is put into the aeration tank, and the second and subsequent aeration tanks are aerated with air or exhaust gas from the aeration tank.

According to the present invention, it is possible to efficiently deodorize odor components in odor waste water and odor gas transferred to exhaust gas at the same time as removing BODXCOD.

Preferred embodiments of the present invention will be described below.

If necessary, heat exchange is performed to reduce the odor-smelling wastewater of the kraft pulp mill, such as liquid blow condensate water and VE drain, to preferably below 40°C, and the pH is preferably from 5 to 9.
The activated sludge is introduced into the aeration tank. This is set in order to perform activated sludge treatment under normal conditions, such as to prevent filamentous bulking, in order to remove BOD at the same time as deodorizing the smelly wastewater.

An aeration tank that performs deodorization using activated sludge can cover the air-open type aeration tank that many factories have as wastewater treatment equipment, and can perform deodorization while removing BOD and COD.

The aeration tank cover section is provided with an inlet and an outlet for odor drainage, activated sludge, and air, and fresh air is introduced into the aeration tank using an exhaust fan and blower.

In the first aeration tank, which is a re-aeration tank that aerates only the activated sludge, air is preferably mixed into the mixed liquid in order to increase the contact efficiency between the odor gas in the exhaust gas and the activated sludge and improve the deodorization rate. The diffused aeration method (hereinafter referred to as water aeration machine) is a method in which air is emitted from the bottom of the tank. Alternatively, it is preferable to install a combination method of aeration and mechanical stirring (hereinafter referred to as surface aerator).

The flow of odor wastewater, activated sludge, air and exhaust gas is parallel flow,
Countercurrent flow is a possibility, but as a result of the study, in order to particularly increase the deodorization efficiency in exhaust gas, activated sludge should be introduced from the first aeration tank, while fresh air and odor-smelling wastewater should be introduced into the second aeration tank. The flow in which the exhaust gas and mixed liquid from the second aeration tank are flowed in parallel from the second aeration tank, and the exhaust gas is finally guided to the first aeration tank to re-aerate the activated sludge in the first aeration tank has the highest deodorization efficiency. was found to be preferable.

If the amount of air is increased, the amount of odor dissipated from the exhaust port will increase, but the dissolved oxygen in the mixed liquid will increase, and the deodorization rate of the odor wastewater will improve. The deodorization rate was high when the amount of odor wastewater treated and the MLSS concentration were low, but this is because when deodorizing with activated sludge using air, the amount of oxygen in the aeration tank tends to be insufficient. It is presumed that the rate as a whole is controlled by the amount of oxygen in the aeration tank.

TR8 sludge loading boat approx. 151! /MLSS-ky・D
In the following cases, it has been found that the deodorization rate increases as the dissolved oxygen in the mixed liquid at the aeration tank outlet increases, and if the dissolved oxygen is 0.5 ppm or more and less than 5 ppm, preferably 90% or more if it is 1.5 ppm or more and less than 5 ppm. It is possible to achieve a deodorization rate of
It is important to increase the odor concentration in treated wastewater and reduce the amount of treated water.

The odor concentration and BOD concentration in odor wastewater are in the positive phase MLSS.
Up to kg/day, no effect of BOD on the deodorization rate was observed. In addition, even if the returned sludge is re-aerated with the odor-containing exhaust gas from the second aeration tank and sent to the second aeration tank, the BO in the aeration tank is
There was no adverse effect on D removal ability at all. This can be solved by covering the open wastewater treatment aeration tank that many kraft pulp factories have and making some modifications.
This means that deodorization treatment can be performed in addition to COD removal, and this is an extremely innovative method for treating odor wastewater without increasing running costs.

The invention will be further explained with reference to the drawings.

FIG. 1 shows an outline of the activated sludge treatment apparatus and the flows of two embodiments. The multi-stage aeration tank consists of three open aeration tanks (1, 2, 3) covered with concrete and has a volume of 1,300 m', and each aeration tank contains activated sludge (1
Surface aerators (4, 5, 6) and submersible aerators (8) for supplying oxygen in the air while thoroughly mixing and stirring 6) and odor wastewater (17), exhaust gas (20) or air ( 19
) to supply the blower (power is installed).

In addition, between each air tank, there are three flow ports (21, 22, 23, 24) for flowing activated sludge (16), mixed liquid (18), air (19), exhaust gas (20), etc. Aeration tank (3)
is provided with an outlet (I5) for the mixed liquid (18).

The aeration tank cover part includes an activated sludge inlet (io), an odor wastewater inlet (11), an air inlet (12), an exhaust port (13),
An exhaust gas pipe (14) and an air supply bypass pipe (25) are provided. An exhaust fan (9) is attached to the exhaust port (13) to introduce fresh air into the aeration tank.O Activated sludge is injected by branching from the existing activated sludge wastewater treatment equipment. , its MLSS concentration was about 15%. After the deodorization treatment, the mixed liquid was again flowed into the aeration tank of the existing wastewater treatment facility for final treatment.

Activated sludge (16), odor wastewater (17) and air (19)
This flow is important for increasing deodorizing efficiency, and examples will be explained individually.

Flow 1 is the first aeration tank (]) of a three-tank aeration tank equipped with a surface aerator (4, 5, 6) and a submersible aerator (8).
There is an activated sludge inlet (10) and an exhaust port (13) in the cover part.
is provided with an exhaust fan (9). Second aeration tank (
2) The cover part has an odor drainage inlet (11) and an exhaust gas pipe (
14), and the exhaust gas pipe (14) is connected via a blower 7) to a submersible aerator (8) installed at the bottom of the first aeration tank (1). The third aeration tank (3) is provided with a mixed liquid outlet (15) and an air inlet (12) in the cover.

Activated sludge branched from existing wastewater activated sludge treatment equipment (
16)-+, from the activated sludge inlet 00) to the first aeration tank (1
), aerate with exhaust gas (20), and exhaust gas (
20) Deodorize the odorous substances inside. Aerated activated sludge (
16) is transferred from the flow port (23) to the second aeration tank (2). The odor waste water (17) is sent from the odor waste water inlet (11) of the second aeration tank (2), and transferred to the second aeration tank while being stirred and mixed with the activated sludge (16) by the surface aerator (5). The mixed liquid (18) is aerated with the exhaust gas from the exhaust tank of the third aeration tank, which enters the third aeration tank (3) through the distribution port (24), and is further aerated with fresh air (19). The mixed liquid from which odor components and BOD have been removed at the same time is discharged through the outlet (15).

Air (19) enters the third aeration tank (3) through the air inlet (12) by the suction force of the exhaust fan (9) provided on the lid of the first aeration tank (1), and then enters the third aeration tank (3) through the air inlet (12). , 21), then is aerated in six tanks and discharged from the exhaust port (13). A part (2o) of the exhaust gas of the second aeration tank (2) is
Aeration is forcibly sent to the submersible aerator (8) of the first aeration tank (1) through the exhaust gas pipe (14) by the force of the blower. Sludge (16)
Only reaeration is required, and the air and exhaust gases are removed from the odor wastewater (
17) and activated sludge (16) in a countercurrent flow direction.

To briefly explain flow 2, activated sludge (16)
is sent to the first aeration tank (1) from the activated sludge inlet (10), is aerated with exhaust gas (20), and then enters the second aeration tank (2) from the distribution port (23), where the odor is removed. The smelly wastewater (17) sent from the wastewater inlet (11) is stirred and mixed by the surface aerator (5), and then transferred to the third aeration tank (3).
The mixture is then discharged from the mixed liquid outlet (15).

Fresh air (19) is supplied to the air inlet (12) provided in the second aeration tank by the suction force of the exhaust fan (9) attached to the first aeration tank (1), and then to the air inlet (12) provided in the second aeration tank, and then to the distribution port. (2
2), passes through the third aeration tank (3), and connects to the air supply bypass pipe (2).
5) or through the exhaust gas pipe (14), the first aeration tank (1)
Enter. Then, it is discharged to the outside of the system from the exhaust port (13).

Figure 2 shows the results of deodorizing VE drain using activated sludge.

It was found that when the TR8 sludge load was approximately 15 g/MTJSS-Y/D or less, it was possible to obtain a deodorization rate of 90 g or more by deodorizing with activated sludge using air.

Of the odor components, fluidized hydrogen is easily deodorized, but in order to achieve a removal rate of 90 or higher for methyl mercaptan, the TREI sludge load was approximately 10#/MLSS-ky-D or less.

The relationship between dissolved oxygen concentration and deodorization rate of the aeration tank outlet mixed liquid is shown in the third section.
As shown in the figure. Approximately 8 if the amount of dissolved oxygen is 0.5 ppm or more
It has been found that if the deodorization rate is 0% and the amount of dissolved oxygen is 1.5 ppm or more, it is possible to obtain a deodorization rate of about 90% or more. The relationship between the BOD removal rate and deodorization rate is shown in Figure 4, which shows that the BOD removal rate and deodorization rate are
:1 relationship was shown.

The influence of the dissolved oxygen concentration of the mixed liquid on the deodorization rate will be further explained with reference to Examples.

Example 1 It was carried out in flow 1. A VE drain from a kraft pulp mill was used as odor wastewater, which was led to a 1100 m three-stage aeration tank for deodorization treatment.

VB drain is 60 rt? /H, TR8 concentration 36.99
/m'.

The temperature was 33°C, the pH was 67, the BO'D was 349 ppm, the activated sludge was heated at 66 m/H, and the air flow was 813 i/H.
As a result of deodorization, the deodorization rate was 80.9%. At this time, the dissolved oxygen in the mixed liquid at the outlet of the aeration tank is Oppm, and the temperature is 28
°C, MLSEI-kf·day, residence time was 8.7 hours, and BOD of treated water was 27 ppm. The activated sludge used was return sludge from a wastewater treatment process using activated sludge at a kraft pulp mill.

Example 2 It was carried out in flow 1. The ``E'' drain of the kraft pulp mill was used as odor wastewater, which was led to a 1,100 m' three-stage aeration tank for deodorization treatment.

WE drain is 70 m/h, TREt concentration is 43.81
1/IIB8b - Mouth temperature is 33°C, pH is 6.3, BO
The deodorization rate was 91.
It was 2%. At this time, the dissolved oxygen in the mixed liquid at the outlet of the aeration tank is 2
．． 5ppmX temperature is 34℃, MLBBp degree is 6200p
pm, TBS sludge load is 10.911/ML8 s
kg/field residence time is 9.3 hours, treated water BOD is 24
It was ppm.

The activated sludge used was return sludge from a wastewater treatment process using activated sludge at a kraft pulp mill.

Example 3 It was carried out in flow 2. Using the Kraft pulp mill's ■E drain as odor wastewater, it was led to a 1100 m three-stage aeration tank and deodorized.

VE drain is 48 trt/H1TR8 concentration 64.11/
/v? XBOD concentration is 258ppm, temperature is 33℃
, pH is 68, activated sludge is 54rr? /H1 air volume is 813 rr? As a result of deodorizing with /H, the deodorization rate was 99
It was 0chi. At this time, the dissolved oxygen in the mixed liquid at the aeration tank outlet was 4.3 ppm, the temperature was 24°C, and the MLSS concentration was 7920.
ppmXTR8 sludge load is 8,! 53 g/MLSS
ky day, residence time is 10.8 hours, BOD of treated water
was 17 ppm. The activated sludge used was return sludge from a wastewater treatment process using activated sludge at a kraft pulp mill.

*MLSS: Sludge concentration in the aeration tank
TR8 sludge load: Reducing sulfur load per gram of unit sludge 92 ※※※BOD sludge load 2 BOD load per unit sludge (m/B) 4 Brief explanation of drawings Figure 1 shows the present invention FIG. 2 is a diagram showing an implementation device and flow. FIG. 2 is a diagram showing the relationship between TR8 sludge load and deodorization rate. FIG. 3 is a diagram showing the relationship between the dissolved oxygen amount (Do) of the mixed liquid and the deodorization rate.

FIG. 4 is a diagram showing the relationship between BOD removal rate and deodorization rate.

The same symbols in the figures refer to the same thing.

1.2,3.・・・・・・First. 2nd and 3rd aeration tanks4.
5,6. ...Surface aerator 7, ...Prower 8, ......'Underwater aerator 9, ...
...exhaust fan】0. ...Activated sludge inlet 11 ・
......Odor wastewater inlet 12, ...
...Air inlet 13 ...Exhaust port 15 ...Mixed flow outlet 16, ...Activated sludge (flow) 17, ...
・・・・・・Odor drainage (flow) 18, ・・・・・・
...Mixed liquid (flow) 19, ...Air (flow) 20 ......Exhaust gas (flow) 21, 22 ...Exhaust gas distribution port 2324・
...Activated sludge, mixed liquid flow port 25, = -1, air supply bypass pipe rice 2 ㎜〆 50 Nirato DOCPPF'0

Claims (1)

[Claims] It has at least two covered aeration tanks, and activated sludge is put into the first aeration tank and aerated with exhaust gas from the second aeration tank, and then the activated sludge in the first aeration tank is aerated with the second aeration tank. Transfer to tank. On the other hand, the odor wastewater is injected into the second aeration tank, and the second and subsequent aeration tanks are aerated using air or exhaust gas, so that the dissolved oxygen in the mixed liquid in the final aeration tank is reduced from 1.5 ppm or more to less than 511) pm. A method for treating odor wastewater characterized by: