JPS6041594A - Treatment of organic waste liquid - Google Patents

Abstract

PURPOSE:To prevent increase of phosphorus load of a treating system and to perform removal of phosphorus always stably by concentrating and separating excess sludge formed by anaerobic-aerobic activated sludge process and dehydrating for specified time after aeration. CONSTITUTION:The liquid 21 to be treated and returned sludge are treated anaerobically in an anaerobic tank 1 by mixing in anerobic state in the absence of dissolved O2, nitrate, and nitrite. The liquid mixture 23 discharged from an anaerobic tank contg. thus increased P and decreased BOD is treated anaerobically in an aerobic tank 2. The liquid mixture 24 discharged from the aerobic tank having decreased BOD and soluble P is separated into treated liquid 25 and settle sludge 22 in a settling basin 3; a part of the sludge 22 is returned to the tank 1 and the rest is charged as excess sludge to a gravity concentration tank 4 to separate it to supernatant liquid 27 and concentrated sludge 28. The sludge 28 is aerated in an aeration tank 5 with O2-contg. gas for <2hr and then dehydrated. Since the concn. of the sludge is high, the time required for absorption of P in the sludge is remarkably reduced. Accordingly, the capacity of the tank 5 is lessened and the amt. of P to be returned from the sludge treating system is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating wastewater containing organic matter and phosphorus, such as domestic sewage, industrial wastewater, and similar organic wastewater. This is related to the improvement of dephosphorization technology.

In general, the anaerobic-aerobic activated sludge method refers to the inflow end of the raw solution in the aeration tank in a conventional activated sludge method facility being kept in an anaerobic state in which dissolved oxygen (DO), nitrate radicals, or nitrite radicals (NOx) are substantially absent. The liquid to be treated and the returned sludge are mixed here, and the mixed liquid is then led to the aerated zone in the latter stage (hereinafter referred to as an aerobic tank) where it is aerated. This technology involves processing and then separating solid-liquid in a sedimentation tank. The process configuration of the anaerobic-aerobic activated sludge method, which has such characteristics, produces activated sludge that has a higher phosphorus uptake capacity than the activated sludge produced by the standard activated sludge method, making it easier to remove pollutants such as BOD and SS. At the same time, most of the soluble phosphorus present in the stock solution can be absorbed into the activated sludge.

The activated sludge produced by this anaerobic-aerobic activated sludge process has a higher phosphorus content than the sludge produced by the standard activated sludge process, and when placed in anaerobic conditions, phosphorus is removed from the sludge. is re-released, and the separated liquid produced in the process of concentrating and dewatering excess sludge contains a high concentration of phosphorus. Therefore, this separated liquid also needs to be treated, and is returned to the inflow end of the treatment system and treated together with the liquid to be treated. However, returning this separated liquid increases the amount of phosphorus that flows into the treatment system, which causes problems in that it reduces the phosphorus removal performance in the anaerobic-aerobic activated sludge process and makes it unstable. .

The present invention aims to provide a method that eliminates these drawbacks of the conventional anaerobic-aerobic activated sludge method, prevents an increase in the amount of phosphorus loaded in the treatment system, and always performs stable phosphorus removal. It is something.

The present invention is characterized in that surplus sludge produced by an anaerobic-aerobic activated sludge method is once concentrated and separated, and the concentrated and separated thickened sludge is aerated in a reaction time of less than 2 hours, and then dehydrated. be.

One embodiment of the present invention will be described based on the drawings. A liquid to be treated 21, which is an organic waste liquid such as domestic sewage, is led to an anaerobic tank 1 together with sedimentation return sludge 22, mixed by an agitator 1', and subjected to anaerobic treatment. . Activated sludge hydrolyzes the high molecular phosphorus compound (BOIJ phosphoric acid) stored in its cells and releases it into the solution, and uses the energy obtained at this time to remove BOD contained in the liquid to be treated. A part of it is taken into the cells and becomes intracellularly stored organic matter. The scale of the anaerobic tank 1 in which this anaerobic treatment reaction takes place varies depending on the composition and concentration of the liquid to be treated 21, but when domestic sewage is used as the liquid to be treated, it is 0.5 to 2. 5 hours is enough.

The anaerobic tank effluent mixed liquid 23 in which soluble phosphorus has increased and BOD has decreased in this way is led to the aerobic tank 2 which is partitioned in a continuous or communicating state. This aerobic tank 2 is aerated by supplying air or other oxygen-containing gas from an aeration diffuser 2', and the activated sludge contained in the anaerobic tank outflow mixed liquid 23 could not be completely absorbed by the anaerobic tank 1. BOD components are ingested and oxidized and decomposed, and the organic matter stored in the cells is also oxidized and decomposed. In addition, the activated sludge utilizes a part of the energy generated during the oxidative metabolism of organic matter to take in soluble phosphorus existing outside the cells, and to add polymeric phosphorus compounds ( Synthesize bo-IJ (IJ acid). At this time, soluble phosphorus in an amount greater than that released in the anaerobic tank 1 is ingested, and the soluble phosphorus concentration in the mixed liquid becomes lower than that in the liquid to be treated.
In order to completely remove soluble phosphorus, the P of the liquid to be treated must be
/BOD ratio is required to be 0.06 or less as a daily average value, and most domestic sewage satisfies this condition. In this case, in order to complete the oxidative decomposition of BOD and the removal of soluble phosphorus, the BOD sludge load F/M ratio of the aerobic tank 2 must be set to 0.
05-07 (1/day), preferably 0.3-o, 5. (
t/day).

The aerobic tank effluent mixed liquid 24 generated in the aerobic tank 2 and reduced in BOD and soluble phosphorus is sent to the settling tank 6 and is separated into solid and liquid into a treated liquid 25 and settled sludge 22.

A part of this settled sludge 22 is returned to the anaerobic tank 1 as return sludge, and the remainder is transferred to the gravity thickening tank 4 as excess sludge 26 and separated into thickening tank supernatant liquid 27 and thickened sludge 28.

Conventionally, when sludge is concentrated using the anaerobic-aerobic activated sludge method, phosphorus is released from the sludge, so the phosphorus concentration in the thickening tank supernatant liquid 27 is considered to be equivalent to the phosphorus concentration in the thickened sludge 28 pore water. The method used was to aerate the excess sludge without concentrating it and absorb the released phosphorus into the sludge. However, in this method, the sludge concentration is low and a large-capacity sludge aeration tank is required, and the amount of air supplied to the aeration tank is also large in order to uniformly aerate the sludge. Furthermore, by aerating the anaerobic sludge, foul-smelling substances such as hydrogen sulfide, ammonia, and butyric acid are dispersed.

However, the concentration tank supernatant liquid 27 in the concentration tank 4 of the present invention
When the distribution of phosphorus in the pore water of the thickened sludge 28 was investigated, the results shown in Figure 3 were obtained. That is, the amount of phosphorus released into the thickening tank supernatant liquid 27 was only 2 to 3 times the amount of phosphorus held in the sludge. Therefore, even if the concentration tank supernatant liquid 27 is directly returned to the anaerobic tank 1, there is almost no effect on the removal of phosphorus.

Next, in the present invention, the thickened sludge 28 separated in the thickening tank 4 is transferred to the sludge aeration tank 5, where it is subjected to an aeration treatment for less than 2 hours.

By the way, the reaction in which phosphorus in the pore water of the thickened sludge 28 is absorbed into the sludge is a -order reaction, as shown in the following equation (1), and as the sludge concentration increases, the time for phosphorus to be absorbed into the sludge increases. If the concentration of the thickened sludge 28 is 1.5% or more, the phosphorus in the pore water of the thickened sludge 28 can be fully reabsorbed into the sludge in less than 2 hours, and the sludge aeration tank 5 Capacity is ~π 1,"? --ku 5a-P (1
) t 1 conversion: Phosphorus uptake rate coefficient of sludge (t/?hr > In the case of the present invention ku = 0.1 ~ 1. Being able to reduce the capacity of the tank 5 not only reduces costs such as construction costs, but also reduces the amount of exhaust gas 5" that is scattered by aerating the sludge.
Hydrogen sulfide and ammonia inside.

This is convenient for removing butyric acid and the like with the deodorizing equipment 6.

Therefore, it is preferable to control the introduction of the oxygen-containing gas 5' into the sludge aeration tank 5 by controlling the dissolved oxygen (Do) concentration in the sludge aeration tank 5 so as to reduce the scattering of malodorous substances as much as possible. That is, the phosphorus uptake reaction of sludge takes 1 minute at DOI~υμ, and if the DO meter 8 detects DO2W/j or more, the amount of oxygen-containing gas 5' introduced can be adjusted using the valve 8'. good.

Particularly, in the present invention, when a gas with an oxygen content of 95 cm or more is used as the oxygen-containing gas 5', the amount of exhaust gas 5'' is even smaller than when air is used, and most of the malodorous substances are decomposed during aeration. Therefore, it is effective in removing malodorous substances.

In this way, in order to reduce the concentration of the oxygen-containing gas 5' in the sludge aeration tank 5 as much as possible to achieve a Do concentration of 1 to 21 JfA, it is better to make the sludge aeration tank 5 a closed type and bring the gas into liquid contact with the surface aeration device 10. preferable.

Further, when the pH in the sludge aeration tank 5 is set to 6 to 9, not only is the proportion of hydrogen sulfide, ammonia, butyric acid, etc. in gaseous form reduced, but the atmosphere is most suitable for sludge absorption of phosphorus. Therefore, it is preferable that the pH meter 9 in the sludge aeration tank 5 controls the amount of pH adjusting chemicals injected into the chemical injection pump 9'.

The aerated concentrated sludge 29 thus aerated in the sludge aeration tank 5 for a reaction time of less than 2 hours is introduced into the dehydrator 7 and dehydrated. The dehydrator 7 is a belt press dehydrator,
Regular dehydrators such as centrifugal dehydrators and vacuum dehydrators are used,
Dehydrated sludge is disposed of by drying, incineration, etc. The dehydrated filtrate 30 from the dehydrator 7 is returned to the anaerobic tank 1 for treatment.

The second illustrated example is basically the same as the first illustrated example, but
A denitrifying rosewood 11 is provided between the anaerobic tank 1 and the aerobic tank 2, and the effluent mixed liquid 23 of the anaerobic tank 1 and the aerobic tank effluent mixed liquid 24 are introduced into the denitrifying rosewood 11 and mixed and stirred. mixed g2
4 is denitrified, and a portion of the soluble phosphorus contained in the anaerobic tank outflow mixed liquid 23 is absorbed into the sludge. Therefore, in the method shown in Figure 2, B in the raw water is
Not only OD and phosphorus removal, but also nitrogen removal becomes possible.

As described above, in the present invention, excess sludge from the settling tank of the anaerobic-aerobic activated sludge method is concentrated and separated, and the concentrated and separated thickened sludge is aerated for a reaction time of less than 2 hours, and then dehydrated. This reduces the phosphorus concentration in the thickening tank supernatant liquid and dewatered filtrate with a small amount of aeration gas, reduces the amount of phosphorus returned from these sludge treatment systems, and improves the anaerobic-aerobic activated sludge treatment system. It is possible to prevent an increase in the amount of phosphorus loaded and to constantly stabilize phosphorus removal.

Next, examples of the present invention will be shown in comparison with comparative examples.

Example 1 Domestic sewage discharged from a residential complex was treated as the liquid to be treated by the method shown in the first illustrated example. The specifications of each device were as follows.

Anaerobic tank: Double cylindrical stirring tank Water capacity 4n? Aerobic tank: 4-panel nitriding rectangular tank 〃 7-settlement pond: Circular clarifier 〃 7-Gravity thickening tank: Circular clarifier tt Q, 5m' water area 0.3m" Sludge aeration 4+1 (4) Cylindrical stirring Aeration tank water volume 1
5 was treated using a sludge aeration tank (8) rectangular oak 1/2501 using such a facility with a volume of treated liquid of 55-A and a return sludge flow rate of 15.4 m'/d, as shown in Table-1. A treatment solution like this was obtained.

Table 1 At this time, the MLSS concentration in the returned sludge was 1.2H, and the MLSS concentration in the aerobic tank was 2800ηβ.

In addition, a portion of the returned sludge was introduced into a gravity thickening tank. The amount of sludge introduced into this gravity thickening tank was 580 t/d. The amount of sludge drawn from the gravity thickening tank is 240 t/d.
As a result, the sludge interface in a gravity thickening tank is 100 m below the water surface.
It was almost constant at 0 m, and the thickened sludge concentration was 2.9%. The sludge concentration distribution and phosphorus concentration distribution in the thickening tank at this time were as shown in FIG.

Furthermore, the thickened sludge from this gravity thickening tank was introduced into a sludge aeration tank, the pH was controlled to 7, and the sludge was aerated with air for 1.5 hours under the conditions of DO1 to 2 WIvt, followed by centrifugal dehydration.

The results are shown in Table 2, and as can be seen from this table, in the case of the present invention, the total phosphorus content in the supernatant liquid and dehydrated filtrate of the gravity thickening tank was 2.11 r/d. Yes, the required air amount is 0
．． It was 15 Ni/d.

Comparative Example-1 Precipitated sludge was introduced into a sludge storage tank, stored anaerobically for 10.3 hours, and then centrifugally dehydrated. The results are shown in Table 2, and the total amount of phosphorus in the dehydrated filtrate in this case is 32.7
It was p/d.

Comparative Example 2 Precipitated sludge was once stored in a 250 t sludge storage tank, and then aerated with air for 10.3 hours in a 250 t capacity sludge aeration tank (B), followed by centrifugal dewatering.

The results are shown in Table 2, and the total amount of phosphorus in the dehydrated filtrate in this case was 3. Although it was small at Or/d, the required air amount was 1. ONm'/d.

As is clear from these results, according to the present invention, the amount of air supplied to the sludge aeration tank is significantly reduced, and the amount of phosphorus in the liquid in the sludge treatment system is small, which can be returned to the anaerobic tank for treatment. However, stable treatment was achieved with minimal increase in phosphorus loading.

Example 2 In place of the air used in the sludge aeration tank in Example 1, pure w1. The raw material was used. Table 3 shows the amounts of malodorous substances released as exhaust gas in this case, Example 1, and Comparative Example 2.

As shown in Table 3, in the case of the present invention, the amount of malodorous substances discharged was significantly reduced compared to Comparative Examples 1 and 2. This indicates that the present invention had a small amount of exhaust gas and was effective in scattering malodorous substances.

[Brief explanation of the drawing]

Fig. 1 is a system explanatory diagram showing one embodiment of the present invention, Fig. 2 is a system explanatory diagram showing another embodiment of the present invention, and Fig. 3 shows water depth, sludge concentration, and total concentration in a gravity thickening tank. FIG. 2 is a diagram showing the distribution of phosphorus concentration. 1...Anaerobic tank, 2...Aerobic tank, 6...Sedimentation tank, 4
... Gravity thickening tank, 5... Sludge aeration tank, 7... Dehydrator, 8... DO meter, 9... pH meter, 11... Denitrification tank, 21... Cover Treatment liquid, 22...Settled sludge, 2
3...Anaerobic tank effluent mixed liquid, 24...Aerobic tank effluent mixed liquid, 25...Treatment liquid, 26...Excess sludge, 27...
- Thickening tank supernatant liquid, 28... Thickened sludge, Shio... Aerated thickened sludge, 30... Dehydrated filtrate.

Claims (1)

[Claims] 1. The rupture solution and return sludge are mixed with dissolved oxygen and nitric acid. Mix in an anaerobic state in which none of the nitrites are substantially present, perform anaerobic treatment, then perform aeration treatment, separate the aerated mixture by precipitation, and use a portion of the separated precipitated sludge as the return sludge and the remainder. A method for treating organic waste liquid, which comprises concentrating and separating the sludge, aerating the separated thickened sludge with an oxygen-containing gas for less than 2 hours, and then dehydrating the sludge. 2. The method for treating organic waste liquid according to claim 1, wherein the concentration of the thickened sludge is at least 1.5%. 3. The method for treating organic waste liquid according to claim 1 or 2, wherein in aeration of the thickened sludge, the dissolved oxygen concentration in the aerated sludge is controlled to 1 to 2 WA. 4. A method for treating organic waste liquid according to claim 1, 2 or 3, wherein a gas having an oxygen content of 95 cm or more is used in aeration of the thickened sludge. 5. The method for treating organic waste liquid according to claim 1, 2, 3, or 4, wherein the pH is controlled to 6 to 9 during aeration of the thickened sludge. 6. Claim 1, wherein the aerated mixture is returned and mixed with the anaerobic treatment mixture to undergo denitrification treatment.
The method for treating organic waste liquid according to item 1, item 2, item 3, item 4, or item 5.